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                UNITED STATES SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 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

________________________________________________________________________________
1.   Name and Address of Reporting Person*

     Tombros                      Peter

- --------------------------------------------------------------------------------
   (Last)                            (First)              (Middle)

     c/o Enzon, Inc.,  20 Kingsbridge Road

- --------------------------------------------------------------------------------
                                    (Street)

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

     Enzon, Inc. (ENZN)

________________________________________________________________________________
3.   I.R.S Identification Number of Reporting Person, if an entity (Voluntary)



________________________________________________________________________________
4.   Statement for Month/Year

     June 30, 2000

________________________________________________________________________________
5.   If Amendment, Date of Original (Mo/Yr)


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

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

     President and Chief Executive Officer
________________________________________________________________________________
7.   Individual or Joint/Group Reporting
     (Check applicable line)

     [X]  Form filed by one Reporting Person
     [_]  Form filed by more than one Reporting Person
________________________________________________________________________________


================================================================================
           Table I -- Non-Derivative Securities Acquired, Disposed of,
                             or Beneficially Owned
================================================================================
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 (Month/ Code Amount or Price (Instr. 3 (I) Ownership (Instr. 3) Day/Year) (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). (Over) SEC 2270 (7-97) 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) $22.3125 07/20/99 A 43,000 (b) 07/08/09 Common 43,000 43,000 D (right to buy) Stock - ------------------------------------------------------------------------------------------------------------------------------------ - ------------------------------------------------------------------------------------------------------------------------------------ - ------------------------------------------------------------------------------------------------------------------------------------ - ------------------------------------------------------------------------------------------------------------------------------------ - ------------------------------------------------------------------------------------------------------------------------------------ - ------------------------------------------------------------------------------------------------------------------------------------ - ------------------------------------------------------------------------------------------------------------------------------------ ====================================================================================================================================
Explanation of Responses: (a) Acquired pursuant to Enzon, Inc's. Non-Qualified Stock Option Plan and qualified under Rule 16b-3. (b) The options vest as to 10,750 shares on each of July 8, 2000, July 8, 2001, July 8, 2002 and July 8, 2003. /s/ Peter Tombros August 9, 2000 - --------------------------------------------- ----------------------- **Signature of Reporting Person Date Peter Tombros ** 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 collection of information contained in this form are not required to respond unless the form displays a currently valid OMB number. Page 2 SEC 2270 (7-97)