AMENDMENT TO EMPLOYMENT AGREEMENT


     Enzon, Inc. (the "Company") and Arthur J. Higgins (the  "Executive")  agree
to amend the Employment  Agreement dated as of May 9, 2001 (the  "Agreement") as
follows:

     1. The first two  sentences  of Section 2 are amended in their  entirety to
read as follows:

          "Unless  terminated  at an earlier date in  accordance  with Section 9
hereof, the term of Executive's  employment hereunder shall commence on the date
agreed upon in writing by Executive  and the Chairman  (the  "Chairman")  of the
Company's  Board of Directors (the  "Board"),  which date shall be no later than
June 15, 2001 (the "Commencement  Date") and shall extend through such date, not
earlier than June 15, 2005,  which is twelve (12) months  following  the date on
which either party hereto  receives  written notice (a "notice of  non-renewal")
from the other  party that such other party does not wish for the term hereof to
continue  beyond such twelve (12) month  period (the  "Term").  In the event the
Commencement  Date does not occur on or before  June 15,  2001,  this  Agreement
shall  terminate and be of no further force or effect and the parties shall have
no obligation to each other under this Agreement or otherwise."

     2. The fourth  sentence of Section  3(a) is amended in its entirety to read
as follows:

          "The Company agrees to cause  Executive to be elected to the Company's
Board as of the Commencement  Date and to cause Executive to be elected to serve
as Chairman at the  meeting of the Board held on the day of the  Company's  next
annual meeting of stockholders, but in no event later than December 31, 2001."

     3. Section 4(e) is amended in its entirety to read as follows:

          "(e) Subject to Executive  commencing his employment  hereunder as the
Company's  President  and Chief  Executive  Officer  on the  Commencement  Date,
Executive shall be granted an option to purchase 400,000 shares of the Company's
Common Stock on the Commencement  Date,  subject to the terms of this Agreement,
the Enzon, Inc. Non-Qualified Stock Option Plan, as amended (the "Option Plan"),
and a Notice of Option  Grant in the form of  Exhibit  A-1  hereto.  Subject  to
Executive  commencing  his employment  hereunder as the Company's  President and
Chief Executive Officer on the Commencement  Date and remaining  employed by the
Company as its President and Chief Executive  Officer through the date Executive
is elected as Chairman of the Board and  Executive  being elected as Chairman of
the  Board,  on the date  Executive  is elected  as  Chairman  of the Board (the
"Election  Date"),  Executive shall be granted an additional  option to purchase
400,000  shares of Common  Stock of the  Company,  subject  to the terms of this
Agreement, the Option Plan and the Notice of Option Grant in the form of Exhibit
A-2  hereto.  The  respective  exercise  prices of the  options  granted  on the
Commencement Date and on the Election Date shall be the last reported sale price
of a share of  Common  Stock as  reported  by the  Nasdaq  Stock  Market  on the
Commencement Date and the Election Date, respectively. The option granted on the
Commencement  Date shall vest and be  exercisable  as to 200,000  shares on such
Date  (subject to the  requirement  in the Option Plan that such  options not be
exercisable for six months after the grant date thereof) and as to 50,000 shares
on each of the first,  second,  third and fourth anniversaries of such Date. The
option  granted on the Election Date shall vest and be exercisable as to 100,000
shares on each of the first, second and third anniversaries of such Date, and as
to 100,000 shares on the fourth


                                       1
<PAGE>

anniversary  of such Date (or such earlier  date,  if any, as the Term ends as a
result of a notice of non-renewal delivered by the Company pursuant to Section 2
hereof).  Notwithstanding the foregoing, each such option shall immediately vest
and become exercisable  (subject to the requirement in the Option Plan that such
options not be exercisable for six months after the grant date thereof) when the
last  reported sale price of a share of the Common Stock is at least one hundred
dollars  ($100.00)  as reported on the Nasdaq  Stock  Market for at least twenty
(20) consecutive trading days after its respective date of grant, provided that,
except as otherwise provided in Section 10 hereof, Executive is then employed by
the Company on a full-time basis as its President and Chief  Executive  Officer.
The price of the Common Stock that triggers  accelerated vesting of such options
shall  be  adjusted  for  stock  splits,   stock  dividends  and  other  similar
recapitalization events. Except as otherwise provided in Section 10 hereof, once
such options become  exercisable they shall remain  exercisable  until 5:00 p.m.
New York City time on the tenth (10th) anniversary of the applicable grant date.
Except as otherwise provided in this Agreement, the Option Plan, a copy of which
Executive has received and reviewed,  shall govern the terms of the options.  In
addition,  at the  discretion  of  the  Board  (or  its  applicable  committee),
Executive shall be entitled to receive further grants of stock options,  subject
to the terms of the Option Plan."

     4. Sections  10(a)(vi) and 10(f)(vii) are both amended in their entirety to
read as follows:

          "all  options  granted to  Executive  pursuant to Section  4(e) hereof
which have not vested at the time of such  termination  will terminate as of the
date of such  termination  and will be of no further  force or effect;  provided
however  that a pro rated  portion  (based on the  portion  of the year  between
anniversaries of the applicable  grant date (i.e., the Commencement  Date or the
Election  Date,  as the case may be) during  which  Executive is employed by the
Company) of the tranche of unvested  options which were scheduled to vest on the
anniversary of the grant date immediately following the date of such termination
shall vest;"

     5.  Exhibit A to the  Agreement  is replaced in its entirety by Exhibit A-1
hereto and a new Exhibit A-2, in the form of Exhibit A-2 hereto, is added to the
Agreement.

     6. Except as amended  hereby,  the Agreement shall remain in full force and
effect.

     7.  This  Amendment  may be  executed  in  counterparts  and  each  of such
counterparts  shall  for all  purposes  be deemed  to be an  original,  and such
counterparts shall together constitute one and the same instrument.

     The parties  hereto have executed this  Amendment as of the 23rd day of May
2001.

                                      ENZON, INC.


                                      By:
                                         ---------------------------------------
                                            Kenneth J. Zuerblis
                                            Vice President, Finance and
                                              Chief Financial Officer

                                      By:
                                         ---------------------------------------
                                             Arthur J. Higgins


                                       2
<PAGE>


Certificate No. ____________                         Optionee: Arthur J. Higgins

No. of options:  400,000       Date granted:  ____________      Price:  ________


     This Option is granted pursuant to the employment agreement dated as of May
     9, 2001, as amended (the "Employment  Agreement")  between the Optionee and
     Enzon Inc. (the "Company").  The Optionee acknowledges receipt of a copy of
     the Enzon  Non-Qualified  Stock Option Plan, as Amended (the  "Plan"),  and
     represents  that he is familiar  with the terms and  provisions of the Plan
     and the Employment  Agreement.  The Optionee hereby accepts this Option and
     agrees that except as otherwise provided in the Employment  Agreement,  the
     Option  Plan shall  govern the terms of the  options  granted  herein.  The
     Optionee  hereby  agrees to accept as  binding,  conclusive,  and final all
     decisions and interpretations of the Compensation Committee or the Board of
     Directors upon any questions  arising under the Plan. As a condition to the
     issuance of shares of Common Stock of the Company  under this  Option,  the
     Optionee authorizes the Company to withhold,  in accordance with applicable
     law from any regular cash  compensation  payable to him, any taxes required
     to be withheld by the Company under Federal, state or local law as a result
     of his  exercise of this  Option.  The  Company,  in its sole and  absolute
     discretion,  may allow  Optionee  to satisfy  Optionee's  federal and state
     income  tax  withholding  obligations  upon  exercise  of the Option by (i)
     having  the  Company  withhold  a portion  of the  shares  of common  stock
     otherwise to be delivered  upon exercise of the Option having a fair market
     value  equal to the amount of federal and state  income tax  required to be
     withheld upon such exercise,  in accordance  with such rules as the Company
     may from time to time  establish,  or (ii) delivering to the Company shares
     of its common  stock other than the shares  issuable  upon  exercise of the
     Option with a fair market  value equal to such taxes,  in  accordance  with
     such rules.


Dated:  [             ]

                                      ENZON, INC.


                                      By:_______________________________________
                                          Name:
                                          Title:


                                      Optionee:


                                      __________________________________________
                                      Arthur J. Higgins



                                   Exhibit A-1

<PAGE>


Certificate No. ____________                         Optionee: Arthur J. Higgins

No. of options:  400,000       Date granted:  ____________      Price:  ________



     This Option is granted pursuant to the employment agreement dated as of May
     9, 2001, as amended (the "Employment Agreement"),  between the Optionee and
     Enzon Inc. (the "Company").  The Optionee acknowledges receipt of a copy of
     the Enzon  Non-Qualified  Stock Option Plan, as Amended (the  "Plan"),  and
     represents  that he is familiar  with the terms and  provisions of the Plan
     and the Employment  Agreement.  The Optionee hereby accepts this Option and
     agrees that except as otherwise provided in the Employment  Agreement,  the
     Option  Plan shall  govern the terms of the  options  granted  herein.  The
     Optionee  hereby  agrees to accept as  binding,  conclusive,  and final all
     decisions and interpretations of the Compensation Committee or the Board of
     Directors upon any questions  arising under the Plan. As a condition to the
     issuance of shares of Common Stock of the Company  under this  Option,  the
     Optionee authorizes the Company to withhold,  in accordance with applicable
     law from any regular cash  compensation  payable to him, any taxes required
     to be withheld by the Company under Federal, state or local law as a result
     of his  exercise of this  Option.  The  Company,  in its sole and  absolute
     discretion,  may allow  Optionee  to satisfy  Optionee's  federal and state
     income  tax  withholding  obligations  upon  exercise  of the Option by (i)
     having  the  Company  withhold  a portion  of the  shares  of common  stock
     otherwise to be delivered  upon exercise of the Option having a fair market
     value  equal to the amount of federal and state  income tax  required to be
     withheld upon such exercise,  in accordance  with such rules as the Company
     may from time to time  establish,  or (ii) delivering to the Company shares
     of its common  stock other than the shares  issuable  upon  exercise of the
     Option with a fair market  value equal to such taxes,  in  accordance  with
     such rules.


Dated:  [              ]

                                      ENZON, INC.


                                      By:_______________________________________
                                          Name:
                                          Title:


                                      Optionee:


                                      __________________________________________
                                      Arthur J. Higgins



                                  Exhibit A-2