U.S. SECURITIES AND EXCHANGE COMMISSION
                              Washington, DC 20549

                                     FORM 5

               ANNUAL STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

    Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934,
       Section 17(a) of the Public Utility Holding Company Act of 1935 or
               Section 30(f) of the Investment Company Act of 1940

[_]  Check box if no longer  subject to Section 16. Form 4 or Form 5 obligations
     may continue. See Instruction 1(b).

[_]  Form 3 Holdings Reported

[_]  Form 4 Transactions Reported

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1.   Name and Address of Reporting Person*

Zuerblis                             Kenneth                 J.
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   (Last)                            (First)              (Middle)

c/o Enzon, Inc., 20 Kingsbridge Road
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                                    (Street)

Piscataway                          New Jersey              08854
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   (City)                            (State)                (Zip)
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2.   Issuer Name and Ticker or Trading Symbol

ENZON, INC. (ENZN)

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3.   IRS Identification Number of Reporting Person, if an Entity (Voluntary)



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4.   Statement for Month/Year

June 30, 2001

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5.   If Amendment, Date of Original (Month/Year)



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6.   Relationship of Reporting Person to Issuer
     (Check all applicable)

     [_]  Director                             [_]  10% Owner
     [X]  Officer (give title below)           [_]  Other (specify below)

     Vice President,
     Finance, Chief
     Financial Officer
     and Secretary
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7.   Individual or Joint/Group Filing
     (Check applicable line)

     [X]  Form filed by one Reporting Person
     [_]  Form filed by more than one Reporting Person
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           Table I -- Non-Derivative Securities Acquired, Disposed of,
                             or Beneficially Owned
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5. 6. 4. Amount of Owner- Securities Acquired (A) or Securities ship Disposed of (D) Beneficially Form: 7. (Instr. 3, 4 and 5) Owned at End Direct Nature of 2. 3. ----------------------------- of Issuer's (D) or Indirect 1. Transaction Transaction (A) Fiscal Year Indirect Beneficial Title of Security Date Code Amount or Price (Instr. 3 (I) Ownership (Instr. 3) (mm/dd/yy) (Instr. 8) (D) and 4) (Instr.4) (Instr. 4) - ------------------------------------------------------------------------------------------------------------------------------------ - ------------------------------------------------------------------------------------------------------------------------------------ - ------------------------------------------------------------------------------------------------------------------------------------ - ------------------------------------------------------------------------------------------------------------------------------------ - ------------------------------------------------------------------------------------------------------------------------------------ - ------------------------------------------------------------------------------------------------------------------------------------ - ------------------------------------------------------------------------------------------------------------------------------------ - ------------------------------------------------------------------------------------------------------------------------------------ - ------------------------------------------------------------------------------------------------------------------------------------ - ------------------------------------------------------------------------------------------------------------------------------------ - ------------------------------------------------------------------------------------------------------------------------------------ - ------------------------------------------------------------------------------------------------------------------------------------ ====================================================================================================================================
* If the form is filed by more than one Reporting Person, see Instruction 4(b)(v). Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly. (Print or Type Responses) (Over) FORM 5 (continued) Table II -- Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities) ================================================================================
9. 10. Number Owner- of ship 2. Deriv- of Conver- 5. 7. ative Deriv- 11. sion Number of Title and Amount Secur- ative Nature or Derivative 6. of Underlying 8. ities Secur- of Exer- Securities Date Securities Price Bene- ity: In- cise 3. Acquired (A) Exercisable and (Instr. 3 and 4) of ficially Direct direct Price Trans- 4. or Disposed Expiration Date ---------------- Deriv- Owned (D) or Bene- 1. of action Trans- of (D) (Month/Day/Year) Amount ative at End In- ficial Title of Deriv- Date action (Instr. 3, ---------------- or Secur- of direct Owner- Derivative ative (Month/ Code 4 and 5) Date Expira- Number ity Year (I) ship Security Secur- Day/ (Instr. ------------ Exer- tion of (Instr. (Instr. (Instr. (Instr. (Instr. 3) ity Year) 8) (A) (D) cisable Date Title Shares 5) 4) 4) 4) - ------------------------------------------------------------------------------------------------------------------------------------ - ------------------------------------------------------------------------------------------------------------------------------------ Common Stock (a) $44.750 7/31/00 A 50,000 (b) 7/31/10 Common 50,000 ---- 50,000 D (right to buy) Stock - ------------------------------------------------------------------------------------------------------------------------------------ Common Stock (a) $44.750 7/31/00 A 50,000 7/31/07 7/31/10 Common 50,000 ---- 50,000 D (right to buy) Stock - ------------------------------------------------------------------------------------------------------------------------------------ - ------------------------------------------------------------------------------------------------------------------------------------ - ------------------------------------------------------------------------------------------------------------------------------------ - ------------------------------------------------------------------------------------------------------------------------------------ - ------------------------------------------------------------------------------------------------------------------------------------ - ------------------------------------------------------------------------------------------------------------------------------------ - ------------------------------------------------------------------------------------------------------------------------------------ - ------------------------------------------------------------------------------------------------------------------------------------ - ------------------------------------------------------------------------------------------------------------------------------------ ====================================================================================================================================
Explanation of Responses: (a) Granted under the Company's Non-Qualified Stock Option Plan and qualified under Rule 16b-3. (b) The options vest as to 10,000 shares on each of July 31, 2001, July 31, 2002, July 31, 2003, July 31, 2004 and July 31, 2005. /s/ Kenneth Zuerblis 7/30/01 - --------------------------------------------- ----------------------- **Signature of Reporting Person Date ** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a). Note: File three copies of this form, one of which must be manually signed. If space provided is insufficient, see Instruction 6 for procedure. Potential persons who are to respond to the collections of information contained in this form are not required to respond unless the form displays a currently valid OMB number Page 2