SCHEDULE 14A INFORMATION

                Proxy Statement Pursuant to Section 14(a) of the
               Securities Exchange Act of 1934 (Amendment No. __ )

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                                   ENZON, INC.
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                (Name of Registrant as Specified In Its Charter)

                             KEVIN T. COLLINS, ESQ.
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                   (Name of Person(s) filing Proxy Statement)

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[LOGO] ENZON, INC. 20 Kingsbridge Road Piscataway, New Jersey 08854 (732) 980-4500 NOTICE OF ANNUAL MEETING OF STOCKHOLDERS TO BE HELD DECEMBER 7, 1999 To our Stockholders: You are hereby notified that the annual meeting of stockholders (the "Annual Meeting") of Enzon, Inc., a Delaware corporation ("Enzon" or the "Company") will be held at the Embassy Suites Hotel, 121 Centennial Avenue, Piscataway, New Jersey on Tuesday, December 7, 1999 at 10:00 a.m. local time, for the following purposes: 1. To elect two Class I directors, each for a term of three years in accordance with the Company's Certificate of Incorporation and By-Laws (Proposal No. 1); 2. To vote on a proposal to approve amendments to the Company's Non-Qualified Stock Option Plan, as amended which would (i) increase the number of shares of Common Stock reserved for issuance upon exercise of options granted to officers, employees, directors and independent consultants under the Non-Qualified Stock Option Plan from 6,200,000 to 7,900,000; and (ii) decrease the number of shares provided for automatic grants of options to the Company's non-employee directors from 60,000 every three years to 10,000 each year (Proposal No. 2); 3. To ratify the selection of KPMG LLP, independent certified public accountants, to audit the consolidated financial statements of the Company for the fiscal year ending June 30, 2000 (Proposal No. 3); and 4. To transact such other matters as may properly come before the Annual Meeting or any adjournment thereof. Only holders of record of the Company's Common Stock, par value $.01 per share, and Series A Cumulative Convertible Preferred Stock, par value $.01 per share, at the close of business on October 28, 1999 are entitled to notice of, and to vote at the Annual Meeting. Enzon hopes that as many stockholders as possible will personally attend the Annual Meeting. Whether or not you plan to attend the Annual Meeting, your proxy vote is important. To assure your representation at the meeting, please complete, sign and date the enclosed proxy card and return it promptly in the enclosed envelope. Sending in your proxy will not prevent you from voting in person at the Annual Meeting. By order of the Board of Directors, John A. Caruso, Secretary Piscataway, New Jersey October 28, 1999

ENZON, INC. ------- PROXY STATEMENT ------- This Proxy Statement is furnished in connection with the solicitation of proxies for use at the annual meeting of stockholders (the "Annual Meeting") to stockholders of record of Enzon, Inc. ("Enzon" or the "Company") as of October 28, 1999, to be held on Tuesday, December 7, 1999 and at any adjournment thereof. The accompanying proxy is solicited by the Board of Directors of the Company and is revocable by the stockholder any time before it is voted. For more information concerning the procedure for revoking the proxy see "General." This Proxy Statement was first mailed to stockholders of the Company on or about November 7, 1999, accompanied by the Company's Annual Report to Stockholders for the fiscal year ended June 30, 1999. The principal executive offices of the Company are located at 20 Kingsbridge Road, Piscataway, New Jersey 08854, telephone (732) 980-4500. OUTSTANDING SHARES AND VOTING RIGHTS Only holders of the Company's common stock, par value $.01 per share (the "Common Stock" or "Common Shares") and Series A Cumulative Convertible Preferred Stock, $.01 per share (the "Series A Preferred Stock" or "Series A Preferred Shares") outstanding at the close of business on October 28, 1999 (the "Record Date") are entitled to receive notice of and vote at the Annual Meeting. As of the Record Date, the number and class of stock that was outstanding and will be entitled to vote at the meeting were 36,813,597 Common Shares and 107,000 Series A Preferred Shares. Each Common Share and Series A Preferred Share is entitled to one vote on all matters. No other class of securities will be entitled to vote at the Annual Meeting. There are no cumulative voting rights. To be elected, a director must receive a plurality of the votes of the Common Shares and Series A Preferred Shares, voting as a single class, present in person or represented by proxy at the Annual Meeting and entitled to vote on the election of directors. The affirmative vote of at least a majority of the Common Shares and Series A Preferred Shares, present in person or represented by proxy at the Annual Meeting and entitled to vote thereon, voting together as a single class, is necessary for approval of Proposal No. 2 and Proposal No. 3. A quorum is representation in person or by proxy at the Annual Meeting of at least one-third of the combined Common Shares and Series A Preferred Shares outstanding as of the Record Date. Pursuant to the Delaware General Corporation Law, only votes cast "For" a matter constitute affirmative votes. Proxy cards which are voted by marking "Withheld" or "Abstain" on a particular matter are counted as present for quorum purposes and for purposes of determining the outcome of such matter, but since they are not cast "For" a particular matter, they will have the same effect as negative votes or votes cast "Against" a particular matter. If a validly executed proxy card is not marked to indicate a vote on a particular matter and the proxy granted thereby is not revoked before it is voted, it will be voted "For" such matter. Where brokers are prohibited from exercising discretionary authority for beneficial owners who have not provided voting instructions (commonly referred to as "broker non-votes"), such broker non-votes will be treated as shares that are present for purposes of determining the presence of a quorum; however, with respect to proposals which require the affirmative vote of a percentage of shares present at the Annual Meeting for approval, such broker non-votes will be treated as not present for purposes of determining the outcome of any such matter. With respect to proposals which require the affirmative vote of a percentage of the outstanding shares for approval, since such broker non-votes are not cast "For" a particular matter, they will have the same effect as negative votes or votes cast "Against" such proposals. 1

PROPOSAL NO. 1 - ELECTION OF DIRECTORS Pursuant to the provisions of the Company's Certificate of Incorporation and By-laws, the Board of Directors is comprised of three classes of directors, designated Class I, Class II and Class III. One class of directors is elected each year to hold office for a three-year term and until successors of such directors are duly elected and qualified. Two Class I directors will be elected at this year's Annual Meeting. The nominees for election to the office of director, and certain information with respect to their backgrounds and the backgrounds of non-nominee directors, are set forth below. It is the intention of the persons named in the accompanying proxy card, unless otherwise instructed, to vote to elect the nominees named herein as Class I directors. Each of the nominees named herein presently serves as a director of the Company. In the event any of the nominees named herein is unable to serve as a director, discretionary authority is reserved to the Board of Directors to vote for a substitute. The Board of Directors has no reason to believe that any of the nominees named herein will be unable to serve if elected. Nominees for Election to the Office of Director at the 1999 Annual Meeting Director Nominee Age Since Position with the Company - ------- --- ----- ------------------------- Peter G. Tombros (1) 57 1994 President and Chief Executive Officer Dr. Rosina B. Dixon (2)(4)(5) 57 1994 Director Non-Nominee Directors Continuing to Serve in the Office of Director After the 1999 Annual Meeting Director Nominee Age Since Position with the Company - ------- --- ----- ------------------------- Randy H. Thurman(1)(2)(6) 50 1993 Chairman of the Board David S. Barlow (2)(4)(7) 43 1999 Director Rolf A. Classon(2)(3)(7) 54 1997 Director Dr. David W. Golde(4)(5)(6) 59 1998 Director Robert LeBuhn (1)(3)(5)(7) 67 1994 Director A.M. "Don" MacKinnon(3)(6) 75 1990 Director (1) Member of the Executive Committee (2) Member of the Compensation Committee (3) Member of the Finance and Audit Committee (4) Member of Scientific Advisory Committee (5) Member of Corporate Governance Committee (6) Class II director serving until the 2000 Annual Meeting (7) Class III director serving until the 2001 Annual Meeting 2

BUSINESS EXPERIENCE OF DIRECTORS Nominee Class I Directors for Election at the 1999 Annual Meeting Peter G. Tombros has served as President and Chief Executive Officer of the Company and a Director of the Company since April 1994. Prior to joining Enzon, Mr. Tombros spent 25 years with Pfizer Inc., a research based, global healthcare company headquartered in New York City. From 1986 to March 1994, he served as a Vice President of Pfizer Inc. in the following areas: Executive Vice President of Pfizer Pharmaceuticals, a division of Pfizer Inc., corporate strategic planning and investor relations. From 1980 to 1986, Mr. Tombros served as Senior Vice President of Pfizer Pharmaceuticals and general manager for the Roerig division of Pfizer Inc. Mr. Tombros currently serves on the Board of Trustees of Cancer Care and the National Cancer Care Foundation and Dominican College. He has been a Director of the American Foundation of Pharmaceutical Education since 1980 and served as Chairman for three of those years. Mr. Tombros serves on the Board of Directors of NPS Pharmaceuticals Inc. and Alpharma Inc. Dr. Rosina B. Dixon has served as a Director of the Company since August 1994. Dr. Dixon has been a consultant to the pharmaceutical industry since 1987. Prior to such time she held senior positions at Ciba-Geigy Pharmaceuticals, a division of Ciba-Geigy Corporation, and Schering-Plough Corporation. She received her M.D. from Columbia University, College of Physicians and Surgeons and is certified by the National Board of Medical Examiners and the American Board of Internal Medicine. She is a member of the American College of Clinical Pharmacology, American Society for Clinical Pharmacology and Therapeutics and the National Association of Corporate Directors and currently serves as a Director of Church & Dwight Co., Inc. and Cambrex Corporation. The Board of Directors recommends a vote FOR Mr. Tombros and Dr. Dixon as Class I Directors (Proposal No. 1 on the Proxy Card). Non-Nominee Class II Director Serving Until the 2000 Annual Meeting Randy H. Thurman has served as the Chairman of the Board of the Company since April 1996 and as a Director of the Company since April 1993. Mr. Thurman is Chairman and Chief Executive Officer of Strategic Reserves, LLC, a company he founded in 1996. Mr. Thurman is the founder and has been Chairman of the Board of Health Care Strategies 2000, a global healthcare consulting firm, since 1995. During 1996, Mr. Thurman also served as a principal of Spencer Stuart Inc. From 1993 to 1995, Mr. Thurman served as Chairman and Chief Executive Officer of Corning Life Sciences. From 1985 to 1993, Mr. Thurman served as Corporate Executive Vice President and a Director of Rhone-Poulenc Rorer, Inc. and President of Rhone-Poulenc Rorer Pharmaceuticals, Inc. He is also Chairman of the Board of UTC International, a wholly owned subsidiary of Donaldson Lufkin Jenrette, and also serves on the Board of Directors of Closure Medical, Inc. A.M. "Don" MacKinnon has served as a Director of the Company since 1990. Mr. MacKinnon was President and Chief Operating Officer of Ciba-Geigy Corporation from 1980 until his retirement in 1986. He was a member of the Board of Directors of Ciba-Geigy Corporation from 1970 until he reached the mandatory retirement age in December 1994. Over the last nine years, Mr. MacKinnon has served on the Board of Directors of several biopharmaceutical companies. Dr. David W. Golde has served as a Director of the Company since March 1998. Dr. Golde has been the Physician-In-Chief at Memorial Sloan-Kettering Cancer Center since 1996. From 1991 to 1996, Dr. Golde served as Head of the Division of Hematology and Oncology at Memorial Sloan-Kettering Cancer Center. Prior to 1991, Dr. Golde was a professor of medicine and Chief of the Division of Hematology and Oncology at UCLA, Director of the UCLA AIDS Center and Director of the UCLA Clinical Research Center. Non-Nominee Class III Directors Serving until the 2001 Annual Meeting David S. Barlow has served as a Director of the Company since June 1999. From 1995 to September 1999 Mr. Barlow was President of Pharmaceuticals at Sepracor, Inc. From 1993 to 1995 Mr. Barlow served as the General Manager of Pharmaceuticals at Sepracor, Inc. Prior to 1993 Mr. Barlow held several senior level positions at Rhone- 3

Poulenc Rorer, Inc., including Vice President, World Wide Marketing and Business Development at Armor Pharmaceutical Company, a subsidiary of Rhone-Poulenc Rorer, Inc. Rolf A. Classon has served as a Director of the Company since January 1997. Mr. Classon is currently an Executive Vice President of Bayer Corporation and President of Bayer Diagnostics. From 1991 to 1995, Mr. Classon was an Executive Vice President in charge of Bayer Diagnostics' Worldwide Marketing, Sales and Service operations. From 1990 to 1991, Mr. Classon was President and Chief Operating Officer of Pharmacia Biosystems A.B. Prior to 1991, Mr. Classon served as President of Pharmacia Development Company Inc. and Pharmacia A.B. Hospital Products Division. Robert LeBuhn has served as a Director of the Company since August 1994. Mr. LeBuhn was chairman of Investor International (U.S.), Inc., a subsidiary of Investor A.B., part of Sweden's Wallenberg Group from June 1992 until his retirement in September 1994, and was its President from August 1984 through June 1992. Mr. LeBuhn is a Director of US Airways Group, Inc., Acceptance Insurance Companies, Inc. and Cambrex Corporation. He is President and a trustee of the Geraldine R. Dodge Foundation. DIRECTORS' COMPENSATION Directors' Cash Compensation During the fiscal year ended June 30, 1999, the Company paid Randy H. Thurman $100,000 in consideration for serving as Chairman of the Board. The Company did not pay cash compensation to its remaining directors for acting as directors or as members of committees of the Board of Directors, other than reimbursement of reasonable expenses incurred by the directors in attending board and committee meetings. Directors' Stock Options In December 1993, the Board of Directors adopted, and the stockholders approved, an amendment to the Non-Qualified Stock Option Plan, as amended, (the "Plan") providing for automatic grants of options ("Automatic Grants") under a formula (the "Formula") to non-executive members of the Board of Directors ("Independent Directors"). Currently under the Formula, Independent Directors automatically receive an option to purchase 60,000 shares of Common Stock on each of the following dates: January 2, 1994, January 2, 1997, January 2, 2000 and January 2, 2003 (the "Regular Grants"). During May 1999, the Board of Directors adopted an amendment to the Formula for grants to Independent Directors, subject to shareholder approval "See Proposal 2." The amendment would reduce the number of shares granted under the Regular Grant to 10,000 shares per year for the years beginning after December 31, 1999 as opposed to the current Formula of 60,000 shares every three years. The options would be granted yearly on January 2 and will vest one year after the grant. Newly elected directors will continue to receive an option to purchase 10,000 shares of Common Stock (the "Initial Election Grant") on the date of each Independent Director's initial election to the Board. In addition each newly-elected Independent Director automatically receives an option to purchase such Independent Director's pro rata share of the Regular Grant, which equals the product of 833 multiplied by the number of whole months remaining in the year until the next Regular Grant (the "Pro Rata Grant"). Those options granted pursuant to a Pro Rata Grant vest and become exercisable on the January 1st following such Independent Director's initial election to the Board. Those options granted pursuant to an Initial Election Grant vest and become exercisable as to 5,000 shares one year after the date of grant; and as to 5,000 shares two years after the date of grant. The per share exercise price of options granted pursuant to the Formula is equal to the fair market value of the Common Stock on the date of grant. An option granted to an Independent Director pursuant to the Formula will not become exercisable as to the relevant shares unless such Independent Director has served continuously on the Board during the period commencing on the date the option was granted and terminating on the date the option is scheduled to vest; provided, however, that if an Independent Director does not fulfill such continuous service requirement due to such Independent Director's death or disability all options granted under the Formula and held by such Independent Director nonetheless vest 4

and become exercisable as though such Independent Director fulfilled the continuous service requirement. An option granted to an Independent Director pursuant to the Formula remains exercisable for a period of ten years from the date of grant. Independent Directors' Stock Plan The Company's 1996 Independent Directors' Stock Plan (the "Independent Directors' Stock Plan") provides compensation to Independent Directors serving on the Board which is paid in the form of the Company's Common Stock. Other than the Chairman of the Board, Independent Directors are not currently entitled to receive cash compensation. Under the Independent Directors' Stock Plan, each Independent Director is entitled to compensation in the form of shares of Common Stock of the Company with a value equal to $2,500 per quarter and $500 for each meeting attended by such Independent Director. The number of shares issued will be based on the last reported sale price of a share of Common Stock on the Nasdaq National Market at the end of the quarter for which fees are payable. During the year ended June 30, 1999, the Company recorded an aggregate of $75,500 in Independent Directors' fees. The following is a summary of compensation paid to the Independent Directors under the Independent Director's Stock Plan: Value of Number Consideration of Shares ------------- --------- Randy H. Thurman $12,500 1,066 Rolf A. Classon 12,500 1,054 Dr. Rosina Dixon 13,000 1,091 David W. Golde 13,000 1,091 Robert LeBuhn 12,500 1,066 A.M. "Don" MacKinnon 12,000 979 Section 16(a) Beneficial Ownership Reporting Compliance Ownership of and transactions in the Company's stock by executive officers and directors of the Company and owners of 10% or more of the Company's outstanding Common Stock are required to be reported to the Securities and Exchange Commission pursuant to Section 16(a) of the Securities Exchange Act of 1934, as amended. During the year ended June 30, 1999 all such reports were filed in a timely manner except (i) Mr. MacKinnon did not file a Form 4 in a timely manner to report the exercise of a stock option and (ii) each of the Independent Directors failed to file a Form 5 in a timely manner to report the shares of Common Stock issued to such Independent Directors under the Independent Directors' Stock Plan during the year ended June 30, 1999. INFORMATION CONCERNING BOARD AND COMMITTEE MEETINGS AND COMMITTEES OF THE BOARD Six meetings of the Company's Board of Directors were held during the fiscal year ended June 30, 1999. A.M. "Don" MacKinnon attended four of the six Board of Directors meetings held. Each incumbent director attended at least 75% of the total number of meetings of the Board of Directors. All incumbent directors attended at least 75% of the total number of meetings of any committees of the Board of Directors, of which such director was a member, held during the fiscal year. As of June 30, 1999, the only standing committees of the Company's Board of Directors were the Finance and Audit Committee, Compensation Committee and Executive Committee. During September 1999 the Board of Directors also created two new committees, a Scientific Advisory Committee and a Corporate Governance Committee. As of June 30, 1999, the Finance and Audit Committee was comprised of Robert LeBuhn, Chairman, and A.M. "Don" MacKinnon. The primary functions of the Finance and Audit Committee are to meet with the Company's independent auditors to discuss and review audit procedures and issues; meet with management on matters concerning 5

the Company's financial condition, internal controls and year-end audit; and report to the Board on such matters. The Finance and Audit Committee held two meetings during the fiscal year ended June 30, 1999. Rolf D. Classon was added to the Finance and Audit Committee in September 1999. As of June 30, 1999, the Compensation Committee was comprised of Dr. Rosina B. Dixon, Chairperson, Rolf A. Classon and Robert LeBuhn. The primary functions of the Compensation Committee are to administer the Company's Non-Qualified Stock Option Plan, determine the compensation of the Company's officers and senior management and review compensation policy. There were three meetings of the Compensation Committee during the fiscal year ended June 30, 1999. During September 1999 Randy H. Thurman and David S. Barlow were appointed to the Compensation Committee and Robert LeBuhn left the Compensation Committee. Rolf A. Classon was named as Chairman of the Compensation Committee in September 1999. The Executive Committee, which as of June 30, 1999 was comprised of A.M. "Don" MacKinnon, Chairman, Peter G. Tombros, and Randy H. Thurman, was established to review and make decisions concerning matters which would otherwise come before the Board, as permitted by Delaware General Corporate Law and the Company's By-laws. Given the relatively small size of the Company's current Board of Directors, the Company determined that efficiencies were not being realized from meetings of the Executive Committee and therefore suspended regular meetings of the Executive Committee in September 1994. There were no meetings of the Executive Committee during the fiscal year ended June 30, 1999. During September 1999 Robert LeBuhn was appointed to the Executive Committee and assumed the role of Chairman of the Executive Committee. Mr. MacKinnon left the Executive Committee in September 1999. The Scientific Advisory Committee is comprised of Dr. David Golde, Chairman, Dr. Rosina Dixon and David S. Barlow. This committee will provide scientific input to the board and serve as the liaison between the Company's senior research and development management and the Board. The Corporate Governance Committee is comprised of Dr. Rosina Dixon, Chairperson, Dr. David Golde and Robert LeBuhn. This committee will review and set corporate governance policy and will be responsible for director and senior management succession planning. COMPENSATION COMMITTEE INTERLOCKS AND INSIDER PARTICIPATION During fiscal year ended June 30, 1999, the members of the Board of Directors serving on the Compensation Committee of the Board of Directors were Dr. Rosina B. Dixon, Chairperson, Rolf A. Classon and Robert Le Buhn, all of whom are non-employee directors of the Company. BUSINESS EXPERIENCE OF EXECUTIVE OFFICERS Set forth below is certain information regarding the executive officers of the Company who do not serve on the Board of Directors. John A. Caruso, 54, has served as Vice President, Administration since May 1998, General Counsel of the Company since July 1994 and as Secretary of the Company since July 1989. From January 1991 to May 1998, Mr. Caruso served as Vice President of Business Development. From January 1991 to July 1994, Mr. Caruso served as Vice President, Legal Affairs of the Company. From the time he joined the Company in September 1987 through December 1990, Mr. Caruso served as Corporate Counsel to the Company. From 1979 through 1987, Mr. Caruso was employed at Baxter Travenol Laboratories in Deerfield, Illinois as corporate counsel. Kenneth J. Zuerblis, 40, has served as Chief Financial Officer since January 1996 and as Vice President, Finance since April 1994. From July 1991 to April 1994, Mr. Zuerblis served as the Company's Controller. From January 1982 to July 1991, Mr. Zuerblis was employed by KPMG LLP. He became a certified public accountant in 1985. 6

SUMMARY COMPENSATION TABLE The following table provides a summary of cash and non-cash compensation for each of the last three fiscal years ended June 30, 1999, 1998 and 1997 with respect to Enzon's Chief Executive Officer and the other executive officers serving during the fiscal year ended June 30, 1999 (the "Named Executive Officers"). Long-Term Compensation Annual Compensation Awards ------------------- ------ Securities Name and Other Annual Underlying All Other Principal Position Year Salary($) Bonus($) Compensation($)(1) Options(#) Compensation($)(2) ------------------ ---- --------- -------- ------------------ ---------- ------------------ Peter G. Tombros 1999 $336,000 $120,000 $ -- 43,000(5) $ 6,152 President and Chief 1998 336,000 70,560 -- 78,000(4) 5,000 Executive Officer 1997 307,626 50,000(3) -- 420,000 4,729 John A. Caruso 1999 175,364 54,000 -- 17,300(5) 1,639 Vice President, Administration, 1998 171,642 26,025 -- 90,000(4) -- General Counsel and Secretary 1997 170,000 25,000 -- 80,000 163 Kenneth J. Zuerblis 1999 165,119 60,000 -- 17,000(5) 4,803 Vice President, Finance and 1998 154,692 33,600 -- 110,000(4) 3,775 Chief Financial Officer 1997 148,052 40,000 -- 90,000 5,395 (1) Excludes perquisites and other personal benefits that in the aggregate do not exceed 10% of the Named Executive Officer's total annual salary and bonus. (2) Consists of annual Company contributions to a 401(k) plan. (3) The payment of Mr. Tombros' bonus, earned for the year ended June 30, 1997, was deferred at his option and paid during the year ended June 30, 1999. (4) Includes stock options granted during July 1998, which represent a portion of the Named Executive Officer's total bonus earned for the year ended June 30, 1998. (5) Represents stock options granted during July 1999, which represent a portion of the Named Executive Officer's total bonus earned for the year ended June 30, 1999. 7

OPTION GRANTS IN LAST FISCAL YEAR The following table contains information concerning the grant of stock options under the Company's Non-Qualified Stock Option Plan to the Named Executive Officers during the fiscal year ended June 30, 1999. Individual Grants ------------------------------------------------ Number of Potential Realizable Value at Assumed Securities % of Total Annual Rates of Stock Price Underlying Options Granted Appreciation for Option Term (3) Options to Employees Exercise or Base Expiration -------------------------------- Name Granted (1) in Fiscal Year Price ($/Share) Date 0%($) 5%($) 10%($) ---- ----------- -------------- --------------- ---- ----- ----- ------ Peter G. Tombros 78,000(2) 17.16% $6.50 7/21/08 0 $318,850 $808,027 John A. Caruso 50,000(2) 11.00% 6.50 7/21/08 0 204,391 517,966 Kenneth J. Zuerblis 70,000(2) 15.40% 6.50 7/21/08 0 286,147 725,153 (1) All options were granted at an exercise price that equaled or exceeded the fair market value of the Common Stock on the date of grant, as determined by the last sale price as reported on the Nasdaq National Market. The options will become exercisable as to all shares immediately upon a "change in control" of the Company as defined in certain agreements between the executive officers and the Company. See "Employment and Termination Agreements." (2) These options were granted during July 1998 as part of the Named Executive Officers total bonus earned for the year ended June 30, 1998 will vest and become exercisable as to 50% of the shares granted on July 21, 1999 and 50% on July 21, 2000, provided that the Named Executive Officer is employed by the Company on the vesting date. (3) The amounts set forth in the three columns represent hypothetical gains that might be achieved by the optionees if the respective options are exercised at the end of their terms. These gains are based on assumed rates of stock price appreciation of 0%, 5% and 10% compounded annually from the dates the respective options were granted. The 0% appreciation column is included because the options were granted with exercise prices which equaled or exceeded the market price of the underlying Common Stock on the date of grant, and thus will have no value unless the Company's stock price increases above the exercise prices. 8

OPTION EXERCISES AND FISCAL YEAR-END VALUES The following table sets forth the information with respect to the Named Executive Officers concerning the exercise of options during the fiscal year ended June 30, 1999 and unexercised options held as of June 30, 1999. Number of Securities Value of Unexercised Underlying Unexercised In-the-Money Options Options at FY-End (#) at FY-End ($)(1) Shares Acquired Value --------------------- ---------------- Name On Exercise (#) Realized($) Exercisable Unexercisable Exercisable Unexercisable ---- --------------- ----------- ----------- ------------- ----------- ------------- Peter G. Tombros -- $ -- 1,069,000 78,000 $18,425,500 $1,096,875 John A. Caruso 75,600 895,671 175,392 70,000 3,043,907 994,375 Kenneth J. Zuerblis 75,000 1,019,065 155,000 90,000 2,498,438 1,275,625 (1) Based upon a market value of $20.56 as determined by the last sale price as reported on the Nasdaq National Market on June 30, 1999. If the exercise price is equal to or greater than such last sale price, the option is deemed to have no value. EMPLOYMENT AND TERMINATION AGREEMENTS The Company has a three-year employment agreement with Peter G. Tombros, which terminates in April 2000, pursuant to which he received an annual base salary of $336,000. In the event Mr. Tombros' employment is terminated for any reason, except if such employment is terminated (i) voluntarily by Mr. Tombros (other than in response to the Company's prior material breach of the employment agreement), (ii) by the Company "for cause" (as defined in the employment agreement) or (iii) as a result of Mr. Tombros' death or disability, Mr. Tombros will be entitled to receive his base salary for one year after such termination. In the event Mr. Tombros' employment is terminated due to his death or disability his base salary will be paid for six months subsequent to such termination. Pursuant to his employment agreement, Mr. Tombros was granted a ten-year option under the Company's Non-Qualified Stock Option Plan to purchase 300,000 shares of the Company's Common Stock at a per share exercise price of $2.69, the fair market value of the Company's Common Stock on the date of grant. The vesting and exercisability of the options granted accelerated in 100,000 share increments when the closing stock price of the Company's common stock, exceeded $4, $5 and $6 per share, for at least twenty consecutive trading days as reported by the Nasdaq National Market. Mr. Tombros' employment agreement also requires him to maintain the confidentiality of Company information and assign inventions to the Company. Mr. Tombros is precluded from competing with the Company during the term of his employment agreement and for two years after his employment is terminated if his employment is terminated by the Company for cause or by Mr. Tombros voluntarily (except in response to the Company's prior material breach of the employment agreement). The Company has agreements with each of its executive officers which provide for payment to each executive officer of three years of compensation and benefits (as defined in such agreements) following a change in control of the Company (as defined in such agreements), including the provision for such payment in the event such executive officer's employment with the Company is terminated under certain circumstances following such change in control. Upon a change in control of the Company, all options held by such executive officers shall vest immediately, notwithstanding any vesting provisions in the option certificates or any plan covering such options. The term of these agreements is for three years. Prior to a change in control of the Company, the agreements automatically renew on each successive anniversary for an additional three years, unless the Company gives the executive officer 60 days notice prior to the anniversary date that it does not plan to renew such contracts. 9

REPORT OF THE COMPENSATION COMMITTEE OF THE BOARD OF DIRECTORS During the fiscal year ended June 30, 1999 the Compensation Committee of the Board of Directors consisted of three non-employee directors. The Compensation Committee determines all compensation paid or awarded to the Company's executive officers, including the Named Executive Officers in the Summary Compensation Table. As with many other biotechnology companies, Enzon's current level of development and the highly volatile nature of biotechnology stocks in general makes executive compensation based on sales and earnings goals or stock performance impracticable. The Compensation Committee believes that an important factor in Enzon's success is the continued development and maintenance of a culture focused on team-oriented performance. In this context, compensation has been based on the accomplishment of a blend of mutually shared and individual goals. The Compensation Committee has reviewed the executive compensation of other biotechnology companies with comparable levels of stockholders' equity and development and has designed the Company's total executive compensation to be targeted at the median of executive compensation levels of these companies. The compensation of the Company's executive officers consist of three principal components: (i) base salary and benefits, (ii) a bonus based on individual contributions evaluated against annual goals and (iii) long-term incentives in the form of stock option grants. The Compensation Committee has established a formal Performance Incentive Program for its executive officers and other members of senior management. The structure and design of the program was based on a detailed study of compensation programs provided at comparable biotechnology companies. During July 1999 the Compensation Committee made certain revisions to the program based upon an updated compensation study. Under the revised program Mr. Tombros can earn a cash bonus of up to a maximum of 40% of his base salary. This was increased from 35% for the fiscal year ended June 30, 1998. Under the amended program Mr. Tombros is also entitled to receive stock option grants to purchase Common Stock of up to a maximum of 1.6 times his base salary divided by the current stock price on the day of grant or approximately 30,400 shares, as compared to a maximum of 130,000 shares in the fiscal year ended June 30, 1998. For the fiscal year ended June 30, 1999 the Compensation Committee used a combination of the previous option calculation under the program and the new calculation to arrive at an option grant of 43,000 shares to Mr. Tombros. The other executive officers, Mr. Caruso and Mr. Zuerblis, can each earn a cash bonus of up to a maximum of 35% of their base salary as opposed to 30% in the fiscal year ended June 30, 1998 and stock option grants to purchase Common Stock. The maximum number of options to purchase shares of Common Stock for each executive officer is calculated based on 1.2 times base salary divided by the price of the Company Common Stock on the date of grant, as compared to 100,000 shares in fiscal 1998. The amount of bonus paid and options granted under the program is based upon the achievement of predetermined corporate and individual objectives. Stock options granted under the program are granted with exercise prices equal to the fair market value of the Company's Common Stock on the date of grant. The annual salary of $336,000 and the bonus awarded to the Company's President and Chief Executive Officer for the fiscal year ended June 30, 1999 were based on Mr. Tombros' extensive prior experience as a senior executive of a major multinational pharmaceutical firm and the compensation paid to chief executive officers with similar credentials at comparable biotech companies. The bonus paid to Mr. Tombros under the Company's Performance Incentive Program was based on many factors including increasing the awareness of the Company in the financial community, the strengthening of the Company's financial position, the renegotiation of the Schering Plough license agreement as well as the progress made by the Company and its partners on products in the Company's development pipeline. During the fiscal year ended June 30, 1999, the Compensation Committee awarded cash bonuses under the program described above to the Company's other executive officers, Messrs. Caruso and Zuerblis. The bonuses were based on the executives' contributions to increase the awareness of the Company in the financial community, the improvement of the Company's financial position and the renegotiation of the Schering-Plough license agreement. 10

The Company also adjusted the salary level of Mr. Caruso and Mr. Zuerblis. The salary adjustments were based on a detailed compensation study of executives with similar credentials at comparable biotechnology companies. THE COMPENSATION COMMITTEE Dr. Rosina B. Dixon, Chairperson Rolf A. Classon Robert LeBuhn STOCKHOLDER RETURN PERFORMANCE GRAPH The graph below summarizes the total cumulative return experienced by the Company's stockholders from June 30, 1994 through June 30, 1999, compared to the Nasdaq National Market-US Index, the Company's former Peer Group index and the Company's new Peer Group index; the Nasdaq Biotechnology Index. During fiscal 1999 the Company changed its Peer Group to the Nasdaq Biotechnology Index. The Company's former Peer Group was not felt to be representative of the Company due to the Company's increase in market capitalization. The former Peer Group consisted of: Isis Pharmaceuticals, Inc., Repligen Corp., Celgene Corp., Gensia Pharmaceuticals Inc., Collagen Corp., Liposome Inc., Cytel Corp., Cytogen Corp., DNAP Holding Corp., (formerly DNA Plant Technology Corp.) and Cephalon Inc. The changes for the periods shown in the graph and table below are based on the assumption that $100 had been invested in Enzon, Inc. Common Stock and in each index below on June 30, 1994. COMPARISON OF FIVE YEAR CUMULATIVE TOTAL RETURN AMONG ENZON, INC., THE NASDAQ NATIONAL MARKET-US INDEX AND PEER GROUPS Fiscal year ending June 30, ------------------------------------------------------------- 1994 1995 1996 1997 1998 1999 ---- ---- ---- ---- ---- ---- Enzon, Inc. 100 86 127 82 232 570 Former Peer Group 100 122 166 104 81 123 Nasdaq National Market-US Index 100 133 171 208 274 394 Nasdaq Biotechnology 100 139 203 213 218 349 Index 11

SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT The following table sets forth certain information concerning stock ownership of all persons known by the Company to own beneficially 5% or more of the outstanding shares of the Company's voting stock, each director, each executive officer named in the Summary Compensation Table and all executive officers and directors of the Company as a group as of October 20, 1999: Percentage of Directors, Officers or Number of Voting Stock 5% Stockholders(1) Shares(2) Outstanding(3) ------------------ --------- -------------- Peter G. Tombros 1,138,300 (4) 3.0% Randy H. Thurman 217,907 (5) * Rolf A. Classon 56,328 (6) * David S. Barlow 124 * Dr. Rosina B. Dixon 128,486 (7) * Dr. David W. Golde 68,498 (8) * Robert LeBuhn 122,979 (9) * A.M. "Don" MacKinnon 153,710(10) * John A. Caruso 223,292(11) * Kenneth J. Zuerblis 213,200(12) * Janus Capital Corporation 2,978,125(13) 8.1% 100 Fillmore Street Denver, Colorado 80206 All Executive Officers and Directors 2,322,824(14) 6.0% as a group (ten persons) - ---------- * Less than one percent. (1) The address of all current executive officers and directors listed above is in the care of the Company. (2) All shares listed are Common Stock. Except as discussed below, none of these shares are subject to rights to acquire beneficial ownership, as specified in Rule 13d-3(d)(1) under the Securities Exchange Act of 1934, as amended, and the beneficial owner has sole voting and investment power, subject to community property laws where applicable. (3) Gives effect to 36,813,597 shares of Common Stock and 107,000 shares of Series A Preferred Stock which were issued and outstanding as of October 20, 1999. Generally, the Series A Preferred Stock and Common Stock will vote as one class of stock. Each share of Common Stock and each share of Series A Preferred Stock is entitled to one vote. The percentage of voting stock outstanding for each stockholder is calculated by dividing (i) the number of shares deemed to be beneficially held by such stockholder as of October 20, 1999 by (ii) the sum of (A) the number of shares of Common Stock outstanding as of October 20, 1999 plus (B) the number of shares of Series A Preferred Stock outstanding as of October 20, 1999 plus (C) the number of shares issuable upon exercise of options or warrants held by such stockholder which were exercisable as of October 20, 1999 or which will become exercisable within 60 days after October 20, 1999. (4) Includes 1,108,000 shares subject to options which were exercisable as of October 20, 1999 or which will become exercisable within 60 days after October 20, 1999. (5) Consists of 200,000 shares subject to options which were exercisable as of October 20, 1999 or which will 12

become exercisable within 60 days after October 20, 1999. (6) Includes 50,000 shares subject to option which were exercisable as of October 20, 1999 or which will become exercisable within 60 days after October 20, 1999. (7) Includes 101,664 shares subject to options which were exercisable as of October 20, 1999 or which will become exercisable within 60 days after October 20, 1999, 500 shares held by Dr. Dixon's husband and 100 shares held by Dr. Dixon's son. Dr. Dixon disclaims beneficial ownership as to shares held by her husband and son. (8) Includes 23,320 shares subject to options which were exercisable as of October 20, 1999 or which will become exercisable within 60 days after October 20, 1999, 32,500 shares held by a separate corporation for Dr. Golde's retirement, 6,700 shares held by three separate trusts for Dr. Golde's children and 1,000 shares beneficially owned by Dr. Golde's wife. (9) Includes 96,664 shares subject to options which were exercisable as of October 20, 1999 or which will become exercisable within 60 days after October 20, 1999. (10) Includes 76,300 shares beneficially owned by Mr. MacKinnon's wife. Mr. MacKinnon disclaims beneficial ownership as to the shares owned by his wife. (11) Consists of 220,992 shares subject to options which were exercisable as of October 20, 1999 or which will become exercisable within 60 days after October 20, 1999. (12) Includes 210,000 shares subject to options which were exercisable as of October 20, 1999 or which will become exercisable within 60 days after October 20, 1999 and 600 shares owned by Mr. Zuerblis' IRA. (13) The information concerning the stock ownership of the Janus Capital Corporation was obtained from a schedule 13F filed by the Janus Capital Corporation with the Securities and Exchange Commission for the period ended June 30, 1999. (14) Includes all shares owned beneficially by the directors and executive officers named in the Summary Compensation table. 13

PROPOSAL NO. 2 - APPROVAL OF AMENDMENT TO THE NON-QUALIFIED STOCK OPTION PLAN In November 1987, the Company's Board of Directors adopted the Non-Qualified Stock Option Plan (the "Plan") in order to enable the Company to attract and retain qualified employees, directors and independent consultants. Subject to stockholder approval, the Board of Directors has approved an amendment to the Plan to increase the total number of Common Stock authorized for issuance upon exercise of options granted under the plan from 6,200,000 to 7,900,000 shares and to provide for Regular Grants of 10,000 options per year to Independent Directors. The Board believes that the best way to attract and retain qualified executives and board members is to offer significant potential rewards based upon the Company's success through the issuance of stock options. The amendment to the Plan increasing the shares of Common Stock authorized for issuance presented herein to the stockholders for their approval is designed to assist the Company in accomplishing this goal. Of the 6,200,000 shares of Common Stock currently authorized, at October 20, 1999, 508,879 shares remained available for future grants. The following summary description of the Plan is qualified in its entirety by the full text of the Plan which may be obtained by the Company's stockholders upon request to the Secretary of the Company. The last sale price of a share of the Company's Common Stock as reported by the Nasdaq National Market on October 20, 1999 was $27.13. Basic Terms Under the Plan, directors, officers and employees of the Company and independent consultants to the Company have been, and will be, eligible for grants of options to purchase shares of Common Stock. To date, all options granted under the Plan have been awarded at the discretion of the Board of Directors or a committee thereof or pursuant to the formulas described below. Currently, the Compensation Committee of the Board of Directors determines who will receive options under the Plan, the number of shares of Common Stock which will be issuable upon exercise of options which are granted under the Plan and the terms of the options granted under the Plan to the extent the terms are not otherwise set forth in the Plan. Currently, no option granted under the Plan may be transferred by the optionee, otherwise than by will or the laws of descent and distribution and, generally, during the optionee's lifetime, the option may be exercised only by the optionee. The exercise price of the options must be at least equal to the fair market value of the underlying Common Stock as of the date of grant. Either the Compensation Committee of the Board of Directors or the Board of Directors may, in its discretion, provide that an option may not be exercised in whole or in part for any specified period or periods of time. No option may be exercised prior to six months from the date of grant except immediately prior to the dissolution or liquidation of the Company or a merger or consolidation where the Company is not the surviving corporation, in which case all outstanding options become immediately exercisable. Options expire no later than the tenth anniversary of the date of grant. Automatic Awards To Independent Directors The Plan currently provides that Independent Directors receive option grants pursuant to the Formula. The Formula provides for Regular Grants of options for 60,000 shares to Independent Directors on each of January 2, 1994, January 2, 1997, January 2, 2000 and January 2, 2003. During May 1999, the Board of Directors adopted a revision to the Formula for grants to Independent Directors, subject to shareholder approval. The amended Formula would reduce the number of shares granted under the Regular Grant to 10,000 shares per year for the years beginning after December 31, 1999 as opposed to the current formula of 60,000 shares every three years. The options will be granted yearly on January 2 and will vest one year after the grant. Newly elected directors will continue to receive the Initial Election Grant on the date of each Independent Director's initial election to the Board. In addition each newly-elected Independent Director automatically receives an option to purchase such Independent Director's pro rata share of the Regular Grant, which equals the product of 833 multiplied by the number of whole months remaining in the year until the next Regular Grant (the "Pro Rata Grant"). Those options granted pursuant to a Pro Rata Grant vest and become exercisable on the January 1st following such Independent Director's initial election to the Board. Those options granted pursuant to an Initial Election Grant vest and become exercisable as to 5,000 shares one year 14

after the date of grant; and as to 5,000 shares two years after the date of grant. The per share exercise price of options granted pursuant to the Formula is equal to the fair market value of the Common Stock on the date of grant. An option granted to an Independent Director pursuant to the Formula will not become exercisable as to the relevant shares unless such Independent Director has served continuously on the Board during the period commencing on the date the option was granted and terminating on the date the option is scheduled to vest; provided, however, that if an Independent Director does not fulfill such continuous service requirement due to such Independent Director's death or disability, all options granted under the Formula and held by such Independent Director shall nonetheless vest and become exercisable as though such Independent Director fulfilled the continuous service requirement. An option granted to an Independent Director pursuant to the Formula will remain exercisable for a period of ten years from the date of grant. Administration The Plan is to be administered by either the Board of Directors or a committee of at least two directors appointed by the Board. The Plan is currently administered by the Compensation Committee. Amendments and Termination Currently, no options may be granted under the Plan beyond November 21, 2007. The Compensation Committee or the Board of Directors may terminate, amend, or revise the Plan with respect to any shares as to which options have not been granted, but may not alter any previously granted options without the optionee's consent. Termination of the Plan will not affect previously granted options. Subject to the foregoing restriction relating to outstanding options, the Board can amend the Plan without stockholder approval unless stockholder approval is required by applicable law or the rules of Nasdaq or any stock exchange on which the Company's shares are then traded. Capital Adjustments The aggregate number of shares of Common Stock available for options, the shares subject to any option, and the price per share, will all be proportionately adjusted for any increase or decrease in the number of issued shares of Common Stock resulting from (1) a subdivision or consolidation of shares or any other capital adjustment, (2) the payment of a stock dividend on the Company's Common Stock, or (3) other increase or decrease in such shares effected without receipt of consideration by the Company. If the Company shall be the surviving corporation in any merger or consolidation, any option outstanding under the Plan shall pertain, apply, and relate to the securities to which a holder of the number of shares of Common Stock subject to the option would have been entitled after the merger or consolidation. Upon dissolution or liquidation of the Company, or upon a merger or consolidation in which the Company is not the surviving corporation, all options outstanding under the Plan shall terminate; except that each optionee shall have the right, immediately prior to such dissolution or liquidation, or such merger or consolidation, to exercise the options that such optionee holds in whole or in part. Tax Consequences An optionee will not recognize taxable income for Federal income tax purposes upon the receipt of an option under the Plan, and the Company will not be entitled to a deduction upon the grant of an option. Upon exercise of an option, the optionee will recognize ordinary income equal to the excess of the fair market value on the date of exercise of the Common Stock received upon exercise over the exercise price for such Common Stock. However, any such optionee who is subject to the trading restrictions of Section 16(b) of the Exchange Act would, unless the optionee elected to recognize ordinary income on the date of exercise, recognize ordinary income on the date such trading restrictions terminate (the "Deferred Date"). The amount of such income would equal the excess of the fair market value on the Deferred Date of the Common Stock received upon exercise of the option over the exercise price for such Common Stock, and the holding period for long-term capital gain treatment would not begin until the Deferred Date. The Company will be entitled to a deduction equal to the amount of ordinary income recognized by any optionee at the same time that such optionee recognized such income. 15

Eligible Participants As of October 20, 1999, there were approximately 95 persons eligible to participate in the Plan. Of these eligible participants, eight are directors (seven of whom are Independent Directors), two are executive officers who are not directors and the remainder are employees of the Company who are not executive officers and consultants. For information concerning options granted under the Plan to directors, the Chief Executive Officer and the Named Executive Officers see "Directors' Compensation - Directors' Stock Options," "Summary Compensation Table" and "Option Grants In Last Fiscal Year." The Board of Directors recommends a vote FOR approval of the proposed amendments to the Non-Qualified Stock Option Plan (Proposal No. 2 on the Proxy Card). PROPOSAL NO. 3 - RATIFICATION OF AUDITORS On October 27, 1999, the Audit Committee of the Board of Directors, pursuant to authority granted by the Board of Directors, approved the retention of KPMG LLP ("KPMG"), independent certified public accountants, to audit the consolidated financial statements of the Company for the fiscal year ending June 30, 2000. KPMG served as auditor of the consolidated financial statements of the Company for the fiscal years ended June 30, 1999, June 30, 1998, and June 30, 1997. Representatives of KPMG are expected to be present at the Annual Meeting and will have the opportunity to make a statement should they desire to do so. Such representatives are also expected to be available to respond to questions. The Board of Directors recommends a vote FOR ratification of the selection of KPMG Peat Marwick LLP, independent certified public accountants, to audit the consolidated financial statements of the Company for the fiscal year ending June 30, 2000 (Proposal No. 3 on the Proxy Card). ANNUAL REPORT TO STOCKHOLDERS The Company's Annual Report to Stockholders for the fiscal year ended June 30, 1999 accompanies this Proxy Statement. STOCKHOLDERS' PROPOSALS It is anticipated that the Company's fiscal 2000 Annual Meeting of Stockholders will be held on or about December 5, 2000. Stockholders who intend to present proposals at such Annual Meeting of Stockholders must submit their proposals to the Secretary of the Company on or before July 5, 2000. 16

GENERAL The cost of soliciting proxies will be borne by the Company. In addition to mailing, proxies may be solicited by personal interview, telephone and telegraph, and by directors, officers and regular employees of the Company, without special compensation therefor. The Company expects to reimburse banks, brokers and other persons for their reasonable out-of-pocket expenses in handling proxy materials for beneficial owners of the Company's Common Stock. Unless contrary instructions are indicated on the proxy card, all Common Shares or Series A Preferred Shares represented by valid proxies received pursuant to this solicitation (and not revoked before they are voted) will be voted FOR the election of the nominees for directors named herein and FOR Proposal No. 2 and Proposal No. 3. Any proxy given pursuant to this solicitation may be revoked by the person giving it at any time before it is voted. Proxies may be revoked by filing with the Secretary of the Company written notice of revocation bearing a later date than the proxy, by duly executing a subsequent proxy relating to the same Common Shares or Series A Preferred Shares or by attending the Annual Meeting and voting in person. Attendance at the Annual Meeting will not in and of itself constitute revocation of a proxy unless the stockholder votes his or her Common Shares or Series A Preferred Shares in person at the Annual Meeting. Any notice revoking a proxy should be sent to the Secretary of the Company, John A. Caruso, at Enzon, Inc., 20 Kingsbridge Road, Piscataway, New Jersey 08854. The Board of Directors knows of no business other than that set forth above to be transacted at the meeting, but if other matters requiring a vote of the stockholders arise, the persons designated as proxies will vote the Common Shares or Series A Preferred Shares represented by the proxies in accordance with their judgment on such matters. If a stockholder specifies a different choice on the proxy, his or her Common Shares or Series A Preferred Shares will be voted in accordance with the specification so made. Please complete, sign and date the enclosed proxy card, which is revocable as described herein, and mail it promptly in the enclosed postage-paid envelope. IT IS IMPORTANT THAT PROXIES BE RETURNED PROMPTLY. WE URGE YOU TO FILL IN, SIGN AND RETURN THE ACCOMPANYING PROXY CARD, NO MATTER HOW LARGE OR SMALL YOUR HOLDINGS MAY BE. By order of the Board of Directors, John A. Caruso, Secretary Piscataway, New Jersey October 28, 1999

Proxy Card ENZON, INC. Annual Meeting of Stockholders December 7, 1999 This Proxy Is Solicited on Behalf of the Board of Directors John A. Caruso and Kenneth J. Zuerblis and each of them, as proxies, with full power of substitution in each of them, are hereby authorized to represent and to vote, as designated below and on the reverse side, on all proposals and in the discretion of the proxies on such other matters as may properly come before the annual meeting of stockholders of Enzon, Inc. (the "Company") to be held on December 7, 1999 or any adjournment(s), postponement(s), or other delay(s) thereof (the "Annual Meeting"), all shares of stock of the Company to which the undersigned is entitled to vote at the Annual Meeting. UNLESS OTHERWISE DIRECTED, THIS PROXY WILL BE VOTED "FOR" PROPOSALS 1, 2 and 3 AND WILL BE VOTED IN THE DISCRETION OF THE PROXIES ON SUCH OTHER MATTERS AS MAY PROPERLY COME BEFORE THE ANNUAL MEETING. THE BOARD OF DIRECTORS RECOMMENDS THAT STOCKHOLDERS VOTE "FOR" PROPOSALS 1, 2 and 3. (1) Election of the following nominees as Class I Directors to serve in such capacities until their successors are duly elected and qualified: PETER G. TOMBROS DR. ROSINA B. DIXON (Authority to vote for any nominee(s) may be withheld by lining through the name(s) of any such nominee(s).) |_| FOR all nominees |_| WITHHOLD authority for all (2) Proposal to approve amendments to the Company's Non-Qualified Stock Option Plan, as set forth in the Company's Proxy Statement dated October 28, 1999. |_| FOR |_| AGAINST |_| ABSTAIN

(3) Ratification of the selection of KPMG LLP to audit the consolidated financial statements of the Company for the fiscal year ending June 30, 2000. |_| FOR |_| AGAINST |_| ABSTAIN |_| Please check this box if you expect to attend the Annual Meeting in person. (Please sign exactly as name appears to the left, date and return. If shares are held by joint tenants, both should sign. When signing as attorney, executor, administrator, trustees or guardian, please give full title as such. If a corporation, please sign in full corporate name by president or other authorized officer. If a partnership, please sign in partnership name by authorized person.) Date:________________________________________________ ----------------------------------------------------- ----------------------------------------------------- Sign Here ----------------------------------------------------- Signature (if held jointly) ----------------------------------------------------- Capacity (Title or Authority, i.e. Executor, Trustee) PLEASE SIGN, DATE AND MAIL YOUR PROXY TODAY.

Appendix A ENZON, INC. NON-QUALIFIED STOCK OPTION PLAN, AS AMENDED/a A. Purpose and Scope The purpose of this Plan is to encourage stock ownership by employees and directors of, and independent consultants to, Enzon, Inc., a Delaware corporation, and its subsidiaries (herein called the "Company"), to provide an incentive to such persons to develop, expand and improve the profits and prosperity of the Company, and to assist the Company in attracting key personnel and consultants through the grant of Options to purchase shares of the Company's Common Stock. B. Definitions Unless otherwise required by the context: 1. "Board" shall mean the Board of Directors of the Company. - ---------- a/ The Plan was amended by vote of the Board of Directors on each of January 10, 1990, February 6, 1990, April 25, 1990, February 23, 1991, May 30, 1991, November 21, 1991, approved by vote of the Stockholders on January 22, 1992, amended by vote of the Board of Directors on December 28, 1992 with such amendment ratified by vote of the Stockholders on February 8, 1993, amended by vote of the Board of Directors on September 13, 1993 with such amendment ratified by vote of the Stockholders on December 7, 1993, amended by the Board of Directors on July 17, 1995 with such amendment ratified by vote of the Stockholders on December 5, 1995, amended by vote of the Board of Directors on October 7, 1997 with such amendment ratified by vote of the Stockholders on December 2, 1997, amended by the Board of Directors on October 20, 1998 with such amendment ratified by vote of the Stockholders on December 1, 1998, amended by the Board of Directors on May 18, 1999 with such amendment to be voted on by the Stockholders on December 7, 1999 (to take effect January 1, 2000). -1-

2. "Committee" shall mean the Compensation Committee, which is appointed by the Board, and which shall be composed of at least two Non-Employee Directors. 3. "Company" shall mean Enzon, Inc. and its subsidiaries. 4. "Code" shall mean the Internal Revenue Code of 1986, as amended. 5. "Independent Director" shall mean a director who is not an employee of the Company. 6. "Non-Employee Director" shall have the meaning ascribed in Rule 16b-3 ("Rule 16b- 3") promulgated under the Securities Exchange Act of 1934, as amended. 7. "Option" shall mean a right to purchase Stock, granted pursuant to the Plan. 8. "Option Price" shall mean the purchase price for Stock under an Option, as determined in Section F below. 9. "Participant" shall mean an employee of the Company, a director of the Company, a consultant to the Company, or any person to whom an Option is granted under the Plan. 10. "Plan" shall mean this Enzon, Inc. Non-Qualified Stock Option Plan, as amended. 11. "Stock" shall mean the Common Stock of the Company, par value $.01. C. Stock to be Optioned Subject to the provisions of Section L of the Plan, the maximum number of shares of Stock that may be optioned or sold under the Plan is 7,900,000 shares. Such shares may be treasury, or authorized but unissued shares of, the Stock of the Company. -2-

D. Administration The Plan shall be administered by the Committee or the Board. Two members of the Committee shall constitute a quorum for the transaction of business. Except as provided in Section Q hereof, the Committee or the Board shall make all decisions with respect to the operation of the Plan, the participation in the Plan by employees or directors of, or consultants to the Company, and with respect to the extent of that participation. The interpretation and construction of any provision of the Plan by the Board or the Committee shall be final. No member of the Board or the Committee shall be liable for any action or determination made by him in good faith. E. Eligibility The Board or the Committee may grant Options to any employee (including an employee who is a director or an officer), or any person who is not an employee who is a director or an officer, or any person who is not an employee and serves as a director of the Company, or any consultant to the Company. Options may be awarded by the Board or the Committee at any time and from time to time to new Participants, or to then current Participants, or to a greater or lesser number of Participants, and may include or exclude previous Participants, as the Board, or the Committee shall determine. Options granted at different times need not contain similar provisions. F. Option Price The purchase price for Stock under each Option shall be at least 100 percent of the fair market value of the Stock at the time the Option is granted, but in no event less than the par value -3-

of the Stock. The fair market value of the Company's Stock shall be determined as follows: a. If the Common Stock continues to be traded on the over-the-counter market as a National Market System Security or is traded on a national securities exchange, the fair market value of the Stock shall be the closing sale price on such day that the Option is granted as reported by the National Association of Securities Dealers Automated Quotation System ("NASDAQ") or the national securities exchange on which the Stock is trading, as the case may be; or b. If the Common Stock ceases to be traded as a National Market System Security but continues to be traded on the over-the-counter market, the fair market value of the Stock shall be the closing bid price on such day that the Option is granted as reported by NASDAQ; or c. If the Common Stock ceases to be traded on the over-the-counter market and is not traded on a national securities exchange, the current market value shall be determined by a reputable investment banking firm retained by the Board. G. Terms and Conditions of Options Except as provided in Section Q hereof, Options granted pursuant to the Plan shall be authorized by the Board or the Committee and shall be evidenced by agreements ("Option Agreements") in such form as the Board or the Committee, shall from time to time approve. Such Agreements shall comply with and be subject to the following terms and conditions: -4-

1. Employment Agreement - The Board or the Committee may, in its discretion, include in any Option granted under the Plan to a Participant who is an employee of the Company a condition that the Participant shall agree to remain in the employ of, and/or to render services to, the Company for a period of time (specified in the Option Agreement) following the date the Option is granted. No such agreement shall impose upon the Company, however, any obligation to employ the Participant for any period of time, except as otherwise agreed to by the Company. 2. Time and Method of Payment - The Option Price shall be paid in full in cash, by certified check or official bank check, at the time an Option is exercised under the Plan. If the Board or the Committee in its sole discretion so authorizes, payment may be made by exchange of shares of the Company's Common Stock previously owned by the optionee, having the same fair market value as determined in the manner set forth in Section F. In addition, at the discretion of the Committee, the optionee may also surrender that number of shares of Common Stock of the Company subject to such option having the aggregate fair market value (as determined in the manner set forth in Section F) equivalent to the aggregate Option Price of the exercised option in lieu of cash payment of the Option Price. Without payment by one of the methods described above, an exercise of any Option granted under the Plan shall be invalid and of no effect. Promptly after the exercise of an Option and the payment of the full Option Price, the Participant shall be entitled to the issuance of a stock certificate evidencing his or her ownership of the Stock issuable under such Option. A Participant shall have none of the rights of a stockholder until the Option is duly exercised, and no adjustment will be made for dividends or other rights for which the record date is prior to the date such Option is duly exercised. -5-

3. Number of Shares - Each Option shall state the total number of shares of Stock to which it pertains. 4. Option Period and Limitations on Exercise of Options - Except for Options granted pursuant to Section Q hereof, the Board or Committee shall determine the period of time during which an Option may be exercised, provided, however, that no Option may be exercised after the expiration of ten years from the date it is granted. Except for Options granted pursuant to Section Q hereof, the Board or the Committee may, in its discretion, provide that an Option may not be exercised in whole or in part for any period or periods of time specified in the Option Agreement; provided, however, that no Option granted subsequent to November 21, 1991 may be exercisable for a minimum of six months from the date of grant. Options granted pursuant to Section Q hereof will be exercisable in accordance with Section R hereof. Except as provided in the Option Agreement and in this Section G(4), an Option may be exercised in whole or in part at any time during its term. No Option may be exercised for a fractional share of Stock. H. Termination of Employment Except as provided in Section I below, if an employee who is a Participant ceases to be employed by the Company, his or her Options unless otherwise exercised, shall terminate as of the close of business on the one hundred and ninetieth (190th) day following the termination of the Participant's employment with the Company; provided, however, that such Participant may exercise his or her Options during such one hundred and ninety (190) day period following such termination of employment only to the extent that he or she would otherwise be entitled to exercise such Options -6-

during such period; provided, further, however, that in no event shall any Option be exercisable more than ten (10) years from the date it was granted. Notwithstanding the foregoing, the Board or the Committee may cancel an Option during the one hundred and ninety (190) day period referred to in this section, if the Participant engages in employment or activities contrary, in the opinion of the Board or the Committee, to the best interests of the Company. The Board or the Committee shall determine in each case whether a termination of employment shall be considered a retirement with the consent of the Company, and, subject to applicable law, whether a leave of absence shall constitute a termination of employment. Any such determination of the Board or the Committee shall be final and conclusive. The foregoing provisions may be modified or waived by the Board or the Committee and do not, in any case, apply to any Participant who is not an employee of the Company. Except for Options granted pursuant to Section Q hereof, the Board or the Committee will determine what, if any, provisions for earlier termination of the Option will be included in the Option Agreement issued to any person who is not an employee. The Board or the Committee will determine who shall be deemed to be an employee of the Company for the purposes of this Section H and Section I below at the time the Option is granted. I. Rights in Event of Death If an employee who is a Participant dies while employed by the Company, or within three months after having retired with the consent of the Company, and without having fully exercised his or her Options, the executors or administrators, or legatees or heirs, of his or her estate shall have the right to exercise such Options to the extent that such deceased Participant was entitled to exercise -7-

the Options on the date of his or her death; provided, however, that in no event shall the Options be exercisable more than ten years from the date they were granted. The foregoing provisions may be modified or waived by the Board or the Committee and do not, in any case, apply to any Participant who is not an employee of the Company. Except for Options granted pursuant to Section Q hereof, the Board or the Committee will determine what, if any, provisions concerning exercise of the Option upon the death of the holder will be included in the Option Agreement issued to any person who is not an employee. J. No Obligations to Exercise Option The granting of an Option shall impose no obligation upon the Participant to exercise such Option. K. Assignability At the discretion of the Committee, Options may be exercised by transferees or beneficiaries who are family members of a Participant. No Option may be pledged, alienated, attached or otherwise encumbered, and any purported pledge, alienation, attachment of encumbrance thereof shall be void and unenforceable against the Company. L. Effect of Change in Stock Subject to the Plan The aggregate number of shares of Stock available for Options under the Plan, the shares subject to any Option, and the price per share, shall all be proportionately adjusted for any increase -8-

or decrease in the number of issued shares of Stock subsequent to the effective date of the Plan resulting from (1) a subdivision or consolidation of shares or any other capital adjustment, (2) the payment of a stock dividend on the Company's Common Stock, or (3) other increase or decrease in such shares effected without receipt of consideration by the Company. If the Company shall be the surviving corporation in any merger or consolidation, any Option shall pertain, apply, and relate to the securities to which a holder of the number of shares of Stock subject to the Option would have been entitled after the merger or consolidation. Upon dissolution or liquidation of the Company, or upon a merger or consolidation in which the Company is not the surviving corporation, all Options outstanding under the Plan shall terminate; provided, however, that each Participant (and each other person entitled under Section I to exercise an Option) shall have the right, immediately prior to such dissolution or liquidation, or such merger or consolidation, to exercise such Participant's Options in whole or in part, notwithstanding any provisions contained in the Plan or the Option Agreement to the contrary. M. Amendment and Termination Subject to the last paragraph of this Section M, the Board or the Committee, by resolution, may terminate, amend, or revise the Plan with respect to any shares as to which Options have not been granted. Neither the Board nor the Committee may, without the consent of the holder of an Option, alter or impair any Option previously granted under the Plan, except as authorized herein. Unless sooner terminated, the Plan shall remain in effect for a period of twenty years from the date -9-

of the Plan's initial adoption by the Board. Termination of the Plan shall not affect any Option previously granted. No such amendment will require stockholder approval, unless stockholder approval is required by either the rules of Nasdaq or any other stock exchange upon which the Company's securities shall be listed or any applicable law. N. Agreement and Representation of Participants As a condition to the exercise of any portion of an Option, the Company may require the person exercising such Option to represent and warrant at the time of such exercise that any shares of Stock acquired at exercise are not registered under the Securities Act of 1933 (the "Act"), are "restricted securities" as that term is defined in Rule 144 under the Act and are being acquired only for investment and without any present intention to sell or distribute such shares, if, in the opinion of counsel for the Company, such a representation is required under the Act or any other applicable law, regulation, or rule of any governmental agency. O. Reservation of Shares of Stock The Company, during the term of this Plan, will at all times reserve and keep available, and will seek or obtain from any regulatory body having jurisdiction any requisite authority necessary to issue and to sell, the number of shares of Stock that shall be sufficient to satisfy the requirements of this Plan. The inability of the Company to obtain from any regulatory body having jurisdiction the authority deemed necessary by counsel for the Company for the lawful issuance and sale of its -10-

Stock hereunder shall relieve the Company of any liability in respect of the failure to issue or sell Stock as to which the requisite authority has not been obtained. P. Effective Date of Plan The Plan shall be effective as of the date it is initially adopted by the Board, provided that Section Q shall not become effective until it has been ratified by the stockholders. Q. Grant of Options to Independent Directors (a) Prior to January 1, 2000 each Independent Director automatically received an Option to purchase 60,000 shares of Stock on each of January 2, 1994 and January 2, 1997 (the "Old Regular Independent Director Grant"). (b) Each Independent Director shall automatically receive, effective as of January 1, 2000, an annual grant of an Option to purchase 10,000 shares of Stock on each January 2 during the Term of this Plan (the "New Regular Independent Director Grant"). Notwithstanding the foregoing, should the date on which a New Regular Independent Director Grant is scheduled to be awarded pursuant to the preceding sentence fall on a Saturday, Sunday or holiday, the New Regular Independent Director Grant shall be awarded on the first business day immediately following such scheduled date. (c) On the date of each Independent Director's initial election to the Board, prior to January 1, 2000, pursuant to a vote of the Company's stockholders or the Board, such newly- elected Independent Director automatically received (i) an Option to purchase a pro rata share of the shares of Stock underlying an Option granted pursuant to an Old Regular Independent Director Grant, which was equal to the product of 1,666 multiplied by the number of whole months remaining in the relevant three year period (the "Old Pro Rata Independent Director Grant"); and (ii) an Option to purchase 10,000 shares of Stock (the "Initial Independent Director Election Grant"). (d) On the date of each Independent Director's initial election to the Board, effective as of January 1, 2000, pursuant to a vote of the Company's stockholders or the Board, such newly- elected Independent Director shall automatically receive (i) an Option to purchase that number of shares of Stock equal to the product of 833 multiplied by the number of whole months remaining in the calender year during which such Independent Director joined the Board (the "New Pro Rata Independent Director Grant"); and (ii) the Initial Independent Director Election Grant. R. Exercise Period of Options Granted to Independent Directors Subject to the last paragraph of this Section R, each Option granted pursuant to the Plan shall vest and become exercisable as follows: (1) Those Options granted pursuant to an Old Regular Independent Director Grant shall vest and become exercisable as to 20,000 shares on the first anniversary of the date of grant; as to 20,000 shares on the second anniversary of the date of grant; and as to the remaining 20,000 shares on the third anniversary of the date of grant. (2) Those Options granted pursuant to an Old Pro Rata Independent Director Grant shall vest and become exercisable as to that number of shares equal to the product of 1,666 multiplied by the number of whole months remaining in the first calendar year in which the Independent Director is elected initially to the Board on the January 1st following such Independent Director's initial election to the Board; and as to any remaining shares in accordance with the schedule for Options granted pursuant to an Old Regular Independent Director Grant as provided in Section R(1) hereof. (3) Those Options granted pursuant to a New Regular Independent Director Grant shall vest and become exercisable on the January 1st following the date on which such Option was granted. (4) Those Options granted pursuant to a New Pro Rata Independent Director Grant shall vest and become exercisable on the January 1st following such Independent Director's initial election to the Board. (5) Those Options granted pursuant to an Initial Independent Director Election Grant shall become exercisable as to 5,000 shares on the first anniversary of the date of grant; and as to 5,000 shares on the second anniversary of the date of grant. -11-

Notwithstanding the foregoing, an Option shall not vest and become exercisable as to the relevant shares unless such Independent Director has served continuously on the Board during the year preceding the date on which such Options are scheduled to vest and become exercisable, or from the date such Independent Director joined the board should such Independent Director have joined the board during such preceding year; provided, however, that if an Independent Director does not fulfill such continuous service requirement due to such Independent Director's death or disability all Options granted to such Independent Director pursuant to Section Q hereof shall nonetheless vest and become exercisable as provided in this Section R. For purposes of this Section R "disability" shall mean a physical or mental condition which prevents an Independent Director from performing his duties as an Independent Director of the Company for a continuous six month period or for a total -12-

of six months during any 18 month period. Any Option which does not vest and become exercisable in accordance with this Section R shall terminate and be of no further force or effect. -13-