Exhibit 4.2

                             CERTIFICATE OF AMENDENT

                                       OF

                          CERTIFICATE OF INCORPORATION

                                       OF

                                   ENZON, INC.

     Enzon,  Inc., a corporation  organized and existing  under and by virtue of
the General Corporation Law of the State of Delaware (the  "Corporation"),  DOES
HEREBY CERTIFY:

     FIRST: That the Board of Directors of said Corporation, at a meeting of its
members,  adopted  resolutions  proposing and declaring  advisable the following
amendments to the Certificate of Incorporation of said Corporation:

     RESOLVED,  that the  first  sentence  of  Article 4 of the  Certificate  of
     Incorporation be amended to read in its entirety as set forth below:

          "4.  Number if Shares.  The total  number of shares of  capital  stock
     which the Corporation shall have authority to issue is sixty-three  million
     (63,000,000)  shares, of which sixty million  (60,000,000)  shares shall be
     Common stock, par value $.01 per share."

     SECOND: That the remainder of Article 4 of the Certificate of Incorporation
of said Corporation shall remain unchanged.

     THRID:  That at the Annual Meeting of Stockholders of the Corporation,  the
holders of a majority of the outstanding stock entitled to vote thereon voted in
favor of said amendments in accordance with the provisions of Section 215 of the
General Corporation Law of the State of Delaware.

     FOURTH: That the aforesaid  amendments were duly adopted in accordance with
the applicable provisions of sections 242 and 216 of the General Corporation Law
of the State of Delaware.


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     IN WITNESS WHEREOF, Enzon, Inc. has caused this certificate to be signed by
Peter G. Tombros, its President and attested to by John A. Caruso,  Secretary of
the Corporation, this 18th of December, 1997.

                                                     By: /s/ Peter G. Tombros
                                                        ------------------------
                                                         Peter G. Tombros
                                                         President

ATTEST

By: /s/ John A. Caruso
    ----------------------
    John A. Caruso
    Secretary

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