Exhibit 10.15

                              EMPLOYMENT AGREEMENT

     Employment  Agreement  dated as of April 5, 1997,  between  Enzon,  Inc., a
Delaware Corporation (the "Company"),  having an address at 20 Kingsbridge Road,
Piscataway, New Jersey 08854, and Peter Tombros ("Executive"), having an address
at 159 Lambert Road, New Canaan, CT 06840.

                                   WITNESSETH:

     WHEREAS,  the Company is a biopharmaceutical  company engaged in developing
advanced therapeutics for life threatening diseases; and

     WHEREAS,   Executive  has  extensive   experience  as  an  executive  of  a
pharmaceutical company and a biopharmaceutical company; and

     WHEREAS,  the Company  desires to continue the  employment of the Executive
and  the  Executive  desires  to  continue  such  employment  on the  terms  and
conditions hereinafter set forth.

     NOW,  THEREFORE,  in  consideration  of the  employment of Executive by the
Company, the above premises and the mutual agreements hereinafter set forth, the
parties hereto agree as follows:

     1.   Duties.

     (a) The Company  employs the Executive as its President and Chief Executive
Officer  and  Executive  accepts  such  employment  subject  to  the  terms  and
conditions  hereof.  As President and Chief Executive  Officer,  Executive shall
have the


                                      E-5


authority  and duty  generally  to  supervise  and  direct the  business  of the
Company,  subject to the control of the Board of Directors  (the "Board") of the
Company and of any duly authorized Committees of the Board.

     (b)  Executive  agrees to  devote  substantially  all of his  time,  during
regular business hours, to the affairs of the Company and shall at all times act
with due regard to the best interests of the Company.

     2.   Noncompetition and Confidentiality.

     (a) The  "Noncompete  Period" shall be (i) the term of this  Agreement and,
(ii)  (A)  the  two  (2)  year  period  immediately   following  termination  of
Executive's  employment  with the  Company  in the event  Executive  voluntarily
terminates his employment, other than pursuant to Section 4(b)(i) hereof, or the
Company terminates  Executive's  employment pursuant to Section 4(b)(ii) hereof,
or (B) any period of time for which the Executive  receives base salary payments
from the  Company  pursuant  to  Section  3(d)  hereof in the event  Executive's
employment  with the Company is  terminated  for any reason which would  entitle
Executive  to base  salary  payments  under  Section  3(d)  hereof  in the event
Executive's  employment  is  Terminated  for  any  reason  which  would  entitle
Executive  to  base  salary  payment  under  Section  3(d)  hereof.  During  the
Noncompete  Period,  Executive will not directly,  or indirectly,  whether as an
officer,  director,  stockholder,   partner,  proprietor,  associate,  employee,
consultant,  representative  or  otherwise,  become  or  be  interested  in,  or
associated with any


                                        2


other person, corporation,  firm, partnership or entity engaged to a significant
degree  in (x)  modifying  enzymes,  protein-based  biopharmaceuticals  or other
pharmaceuticals  in a  manner  similar  to that  described  in U.S.  Patent  No.
4,179,337,   or  U.S.  Patent  No.   4,946,778,   (y)  developing   single-chain
antigen-binding  proteins or (z) any technology or area of business in which the
Company  becomes  involved  to a  significant  degree  during  the  term of this
Agreement.  For  purposes of the  preceding  sentence to  determine  whether any
entity is engaged in such activities to a "significant  degree"  comparison will
be made to the Company's operations at that time. In other words, an entity will
be deemed to be engaged in an activity to a significant  degree if the number of
employees  and/or amount of funds devoted by such entity to such activity  would
be  material  to the  Company's  operations  at that time.  Executive  is hereby
prohibited from ever using any of the Company's proprietary information or trade
secrets to conduct  any  business.  The  provision  contained  in the  preceding
sentence shall survive the  termination of  Executive's  employment  pursuant to
Section  4 hereof  or  otherwise.  In the event  Executive  breaches  any of the
covenants  set  forth  in this  Section  2(a),  the  running  of the  period  of
restriction set forth herein shall recommence upon  Executive's  compliance with
the terms of this Section 2(a).

     (b) Executive  recognizes and acknowledges that information relating to the
Company's  business,  including,  but not  limited to,  information  relating to
patent applications filed or to be filed by the Company,  trade secrets relating
to the


                                        3


Company's  products or  services,  and  information  relating  to the  Company's
research and development activities,  shall be and remain the sole and exclusive
property  of the Company  and is a  valuable,  special  and unique  asset of the
Company's  business.  The  Executive  will not,  during or after the term of his
employment  by the  Company,  disclose  any  such  information  to  any  person,
corporation,  firm,  partnership  or  other  entity;  provided,  however,  that,
notwithstanding  the foregoing,  during the term of Executive's  employment with
the Company,  Executive may make such  disclosure  if such  disclosure is in the
Company's best interests,  is made in order to promote and enhance the Company's
business, and sufficient arrangements are made with the person or entity to whom
such disclosure is made to ensure the  confidentiality  of such disclosure.  The
provisions of this Section 2(b) shall  survive the  termination  of  Executive's
employment pursuant to Section 4 hereof or otherwise.

     (c) Executive  agrees that the covenants and  agreements  contained in this
Section 2 are the  essence of this  Agreement;  that each of such  covenants  is
reasonable  and  necessary  to protect and  preserve  the  Company's  interests,
properties and business;  that  irreparable  loss and damage will be suffered by
the Company should Executive  breach any of such covenants and agreements;  that
given the unique nature of the Company's  business such loss and damage would be
suffered  by the  Company  regardless  of where a breach of such  covenants  and
agreements  occur,  thus,  making  the  absence  of  a  geographical  limitation
reasonable; that


                                        4


each of such  covenants and  agreements is separate,  distinct and severable not
only from the other of such covenants and agreements but also from the other and
remaining  provisions of this Agreement;  that the unenforceability or breach of
any such covenant or agreement  shall not affect the validity or  enforceability
of any  other  such  covenant  or  agreement  or any  other  provision  of  this
Agreement;  and that, in addition to other remedies available to it, the Company
shall be entitled to both  temporary  and  permanent  injunctions  and any other
rights or  remedies  it may have,  at law or in  equity,  to prevent a breach or
contemplated   breach  by  Executive  of  any  such   covenants  or  agreements.
Notwithstanding  anything  herein to the contrary,  if a period of time or other
restriction  specified in this Section 2 should be determined to be unreasonable
in a judicial proceeding,  then the period of time or other restriction shall be
revised so that the covenants contained in this Section 2 may be enforced during
such period of time and in  accordance  with such other  restrictions  as may be
determined to be reasonable.

     (d)  Executive  agrees to assign and does hereby  assign to the Company all
tangible and intangible  property,  including,  but not limited to,  inventions,
developments or discoveries conceived, made or discovered by Executive solely or
in collaboration with others during the term of Executive's  employment with the
Company, which relate in any manner to the Company's business.


                                        5


     3. Compensation and Other Benefits.

     For all services rendered by Executive and all covenants  undertaken by him
pursuant to this  Agreement,  the Company shall pay, and Executive shall accept,
the compensation set forth in this Section 3.

     (a)  Executive  shall  receive  an  annual  base  salary  of Three  Hundred
Thirty-Six  Thousand  Dollars   ($336,000.00)  during  the  term  of  employment
hereunder, payable in accordance with the Company's normal payroll practices for
its senior  management.  The Company may, at any time, in the  discretion of the
Board,  increase,  but not  decrease,  Executive's  base  salary in  response to
increases  in the cost of living or based  upon  merit as a result of a positive
review of Executive's  performance by the Board.  Executive shall be entitled to
begin receiving his salary hereunder on the Effective Date.

     (b) Executive  shall be entitled to  participate  in the Senior  Management
Performance  Incentive  Program,  as  approved  by  the  Board  or  Compensation
Committee and any other incentive program hereafter established and available to
executive  officers of the Company (the "Program").  There shall be no guarantee
that any  payment or grant of options  shall be made  under the  Program,  and a
payment or grant of options in one year does not imply that a similar payment or
grant, or any payment or grant, will be made in subsequent years.

     (c) In addition to any options  which may be granted to Executive  pursuant
to Section 3(b) hereof, Executive is


                                        6


hereby  granted  options to  purchase  an  aggregate  of  300,000  shares of the
Company's common stock,  $.01 par value (the "Common Stock") under the Company's
Non-Qualified  Stock Option Plan, as amended (the  "Non-Qualified  Plan") at the
per share exercise price equal to the closing price of the Common Stock on April
15, 1997.  Such  options  shall vest and become  exercisable  as to such 300,000
shares of Common Stock on April 5, 2002,  if,  except as  otherwise  provided in
Section  3(d),  Executive  shall  then be  employed  by the  Company;  provided,
however,  that such options  immediately shall vest and become  exercisable upon
the occurrence of each of the respective events described below,  provided that,
except as otherwise provided in Section 3(d),  Executive is then employed by the
Company,  in which  case such  options  will vest as to the number of shares set
forth  opposite each such event (the  "Accelerated  Vesting  Schedule").  In any
event such  options  shall be  exercisable  as to each  tranche of shares in the
event of accelerated  vesting pursuant to the Accelerated Vesting Schedule or as
to the entire 300,000 shares in the event there is no such  accelerated  vesting
for a term  of  five  (5)  years  from  the  respective  date  of  vesting  (the
"Expiration  Date").  Such options shall be represented by a NonQualified  Stock
Option  Certificate  (the "Option  Certificate")  in the form attached hereto as
Exhibit A.


                                        7


   Options                                      Event
   -------                                      -----

100,000 shares                Such  options  shall vest and  become  exercisable
                              when the closing  price of the Common  Stock is at
                              least  four  dollars  ($4.00) as  reported  on the
                              NASDAQ  National  Market for at least  twenty (20)
                              consecutive trading days.

100,000 shares                Such  options  shall vest and  become  exercisable
                              when the closing  price of the Common  Stock is at
                              least  five  dollars  ($5.00) as  reported  on the
                              NASDAQ  National  Market for at least  twenty (20)
                              consecutive trading days.

100,000 shares                Such options shall vest and become  exercisable as
                              when the closing  price of the Common  Stock is at
                              least  six  dollars  ($6.00)  as  reported  on the
                              NASDAQ  National  Market for at least  twenty (20)
                              consecutive trading days.


The  prices and number of shares set forth  above  shall be  adjusted  for stock
splits, stock dividends and other similar recapitalization events.

     (d) In the event the Company terminates  Executive's  employment  hereunder
for any reason, except "For Cause" pursuant to Section 4(b)(ii) hereof or due to
Executive's  Disability  or Death  pursuant  to Sections  4(b)(iii)  or 4(b)(iv)


                                       8 



hereof, respectively,  or Executive terminates his employment hereunder pursuant
to Section 4(b)(i) hereof, prior to the second anniversary of the Effective Date
(the  "Second  Anniversary  Date"),  Executive  shall  receive  either  (A)  the
remainder of his base salary  hereunder  payable through the Second  Anniversary
Date or (B) his base salary hereunder payable for one year immediately following
such  termination,  whichever  shall  be  greater.  In  the  event  the  Company
terminates Executive's employment for any reason, except "For Cause" pursuant to
Section  4(b)(ii)  hereof or due to Executive's  Disability or Death pursuant to
Sections 4(b)(iii) or 4(b)(iv) hereof, respectively, or Executive terminates his
employment  hereunder  pursuant to Section  4(b)(i)  hereof,  subsequent  to the
Second  Anniversary  Date,  Executive  shall  receive his base salary  hereunder
payable for one year  immediately  following such termination or until Executive
becomes  otherwise  employed on a full-time basis,  whichever is sooner.  In the
event the Executive's  employment with the Company is terminated for any reason,
except for Employee's  voluntary  resignation  or pursuant to Section  4(b)(ii),
(iii) or (iv) hereof,  the options granted pursuant to Section 3(c) hereof which
are  exercisable at the time of such  termination  (the "Vested  Options") shall
remain  exercisable  during the relevant exercise period or periods set forth in
Section 3(c) hereof and those  options  granted  pursuant to Section 3(c) hereof
which  are not  exercisable  at the time of such  termination  (the  "Non-Vested
Options") shall become  exercisable in accordance  with the Accelerated  Vesting
Schedule provisions of


                                        9


Section 3(c) in the same manner as if the  Executive's  employment  had not been
terminated;  provided that all such Non-Vested  Options will terminate and be of
no  further  force and  effect to the  extent  such  options  have not vested in
accordance with the Accelerated  Vesting  Schedule on or prior to April 5, 2002.
In the event the Company terminates  Executive's employment "For Cause" pursuant
to Section 4(b)(ii) hereof or Executive  terminates his employment hereunder for
any reason other than as provided in Section  4(b)(i)  hereof,  Executive  shall
receive no further payments from the Company,  all Vested Options at the time of
such termination shall remain exercisable during the relevant exercise period or
periods set forth in Section 3(c) and those options granted  pursuant to Section
3(c) hereof which are Non-Vested  Options at the time of such termination  shall
terminate  immediately  as of the  date  of such  termination.  All  salary  and
severance payments made to Executive  hereunder shall be made in accordance with
the Company's normal payroll practices for senior management.

     (e) In the event  the  Company  terminates  Executive's  employment  due to
Executive's  Disability  pursuant to Section  4(b)(iii) of this  Agreement,  the
Company  shall pay to  Executive,  during the six-month  period  following  such
termination,  an amount equal to the difference between  Executive's base salary
hereunder for such six months (exclusive of benefits) and the amount received by
Executive  during such  six-month  period under any employee  disability  policy
maintained  by the  Company  for the benefit of  Executive.  The  Company  shall
calculate and pay any


                                       10


amounts due herein no less  frequently  than  semi-monthly.  The options granted
pursuant  to Section  3(c) hereof  which are Vested  Options at the time of such
termination  shall remain  exercisable  during the relevant  exercise  period or
periods set forth in Section 3(c) hereof and a pro rata portion  (based upon the
number of days which have  elapsed at the time of such  termination  in the five
(5) year period  commencing on the Effective Date and ending on May 5, 2002 (the
"Vesting  Period")) of the options which are  Non-Vested  Options at the time of
such termination shall become exercisable immediately upon such termination. For
example,  if such termination  occurs 50% of the way through the Vesting Period,
50% of the total number of Non-Vested Options shall vest and become exercisable.
It is acknowledged and agreed that the immediately  preceding  sentence shall be
deemed a waiver and modification of the restrictions  imposed on the exercise of
options in the event of disability under Section H of the Non-Qualified Plan and
that  such  waiver  and   modification   was  authorized  and  approved  by  the
Compensation  Committee of the Board (the "Committee") as permitted by Section H
of the Non-Qualified Plan.

     (f) In the event  Executive's  employment  is  terminated  due to his death
pursuant  to  Section  4(b)(iv)  of this  Agreement,  the  Company  shall pay to
Executive's  estate,  during the six-month  period  following such  termination,
Executive's base salary  hereunder for such six months  (exclusive of benefits).
The options granted pursuant to Section 3(c) hereof which are Vested


                                       11


Options at the time of such  termination  shall  remain  exercisable  during the
relevant  exercise  period or periods set forth in Section 3(c) hereof and a pro
rata  portion  (based upon the number of days which have  elapsed at the time of
such  termination  in the Vesting  Period) of the options  which are  Non-Vested
Options at the time of such  termination  shall become  exercisable  immediately
upon such termination and shall remain  exercisable for the five (5) year period
commencing on such date of termination.  For example, if such termination occurs
50% of the way through the Vesting Period, 50% of the total number of Non-Vested
Options shall vest and become  exercisable.  It is acknowledged  and agreed that
the  immediately  preceding  sentence  shall  be  deemed  to  be  a  waiver  and
modification of the restrictions imposed on the exercise of options in the event
of death  under  Section I of the  Non-Qualified  Plan and that such  waiver and
modification  was  authorized  and  approved by the  Committee  as  permitted by
Section I of the Non-Qualified Plan.

     (g) In the event of a Change of  Control,  the Change of Control  Agreement
dated as of January 20, 1995, between Executive and Company shall govern, except
as  specifically  set forth  herein  with  respect  to the  options  granted  to
Executive  pursuant to Section  3(c)  hereof.  For  purposes  hereof  "Change of
Control" shall mean: (i) A "Board Change" which, for purposes of this Agreement,
shall have  occurred if a majority of the seats (other than vacant seats) on the
Company's  Board  were to be  occupied  by  individuals  who  were  neither  (A)
nominated  by a  majority  of the  Incumbent  Directors  nor  (B)  appointed  by
directors so nominated. An "Incumbent Director" is a member of the Board who has
been either (A) nominated by a


                                       12


majority of the  directors  of the Company  then in office or (B)  appointed  by
directors so nominated,  but excluding,  for this purpose,  any such  individual
whose  initial  assumption  of office  occurs as a result of either an actual or
threatened election contest (as such terms are used in Rule 14a-11 of Regulation
14A  promulgated  under the  Securities  Exchange  Act of 1934,  as amended (the
"Exchange  Act")) or other  actual or  threatened  solicitation  of  proxies  or
consents by or on behalf of a Person (as defined  herein)  other than the Board;
or (ii) the acquisition by any  individual,  entity or group (within the meaning
of Section  13(d)(3) or 14(d)(2) of the Exchange Act) (a "Person") of beneficial
ownership  (within the meaning of Rule 13d-3 promulgated under the Exchange Act)
of a majority of the then  outstanding  voting  securities  of the Company  (the
"Outstanding Company Voting Securities");  provided, however, that the following
acquisitions  shall not constitute a Change of Control:  (A) any  acquisition by
the Company,  or (B) any  acquisition  by any employee  benefit plan (or related
trust)  sponsored or maintained by the Company or any corporation  controlled by
the Company,  or (C) any public offering or private  placement by the Company of
its voting  securities;  or (iii) a merger or  consolidation of the Company with
another entity in which neither the Company nor a corporation that, prior to the
merger or consolidation, was a subsidiary of the Company, shall be


                                       13


the surviving entity; or (iv) a merger or consolidation of the Company following
which  either  the  Company  or a  corporation  that,  prior  to the  merger  or
consolidation,  was a subsidiary of the Company,  shall be the surviving  entity
and a majority of the Outstanding Company Voting Securities is owned by a Person
or Persons who were not  "beneficial  owners" of a majority  of the  Outstanding
Company Voting Securities immediately prior to such merger or consolidation;  or
(v) a voluntary or  involuntary  liquidation  of the Company;  or (vi) a sale or
disposition by the Company of at least 80% of its assets in a single transaction
or a series of  transactions  (other than a sale or  disposition  of assets to a
subsidiary of the Company in a transaction  not involving a Change of Control or
a change in control of such subsidiary).  If any of the Change in Control events
specified in (iii),  (v) or (vi) above occur,  any options  granted  pursuant to
Section 3(c) hereof which are  Non-Vested  Options as of the  effective  date of
such Change in Control event shall vest immediately prior to such effective date
(and Employee will be provided a reasonable opportunity to exercise such options
prior to such effective date) to the extent provided in the Accelerated  Vesting
Schedule to the extent the  shareholders  of the  Company  receive a payment for
their shares of Common  Stock in  connection  with such Change in Control  event
which is equal to the closing price levels set forth in the Accelerated  Vesting
Schedule.  In the event any of the Change in Control events  specified in (iii),
(v) or (vi) above occur, all Vested Options and Non-Vested Options granted under
Section 3(c)


                                       14


shall  terminate as of the effective date of such Change in Control event to the
extent  not  previously  exercised.  If any  of the  Change  in  Control  events
specified in (i),  (ii) or (iv) above  occur,  the options  granted  pursuant to
Section 3(c) hereof which are Vested  Options as of the  effective  date of such
Change in Control event shall remain  exercisable  during the relevant  exercise
period or periods  set forth in Section  3(c) hereof and those  options  granted
under Section 3(c) hereof which are Non-Vested  Options as of the effective date
of such Change in Control shall become  exercisable  and remain  exercisable  in
accordance with the Accelerated  Vesting Schedule  provisions of Section 3(c) in
the  same  manner  as  if  such  Change  in  Control  event  had  not  occurred.
Notwithstanding any provisions  contained in Section L of the Non-Qualified Plan
or in the Option  Certificate  pertaining to the exercise of the options granted
pursuant to Section 3(c) hereof, if any of the events specified in (iii), (v) or
(vi) above occur the provisions contained herein shall apply.

     (h) Executive  shall be entitled to vacations in accordance with the policy
of the Company  with  respect to its senior  management,  in effect from time to
time and shall be eligible to  participate  in any  pension,  profit  sharing or
similar plan and any health,  hospitalization,  medical,  accident,  disability,
sick leave,  supplementary  income  benefit,  life  insurance  or other  similar
benefit plan or program of the Company now existing or hereafter established and
available to the Company's  employees  generally or to key employees as a group,
in


                                       15


all  cases to the  extent  his age,  health  and other  qualifications  make him
eligible to  participate.  Executive  also shall be entitled to such  additional
benefits  as may be  granted  to him from  time to time by the  Board.  Upon the
termination  of  Executive's  employment  for any reason,  the Company shall pay
Executive for any unused accrued vacation time.

     (i) Executive shall be reimbursed for reasonable travel,  entertainment and
other expenses associated with the performance of his duties hereunder, promptly
upon his delivery of appropriate receipts and other documentation evidencing the
incurrence of such expenses.


     (j) All compensation payable and other benefits provided under this Section
3 shall be subject to  customary  withholding  for  income,  F.I.C.A.  and other
employment taxes.

     (k) All  options  granted  pursuant  to this  Section  3 shall be issued in
accordance with and be subject to the terms and conditions of the  Non-Qualified
Plan.  Except as  otherwise  specifically  set forth  herein,  if there exists a
conflict  between  the  terms of the  Non-Qualified  Plan and the  terms of this
Agreement,  the terms of the Non-Qualified  Plan shall govern. If there exists a
conflict  between the terms of this  Agreement and the Option  Certificate,  the
Option  Certificate shall govern.  Executive has reviewed the Non-Qualified Plan
and the form of the Option Certificate prior to executing this Agreement.


                                       16


     (l) All  options  and  terms  and  conditions  pertaining  thereto  granted
pursuant to this  Section 3 shall  extend  beyond the  Termination  Date of this
Agreement.

     4.   Term and Termination of this Agreement

     (a) The term of employment  pursuant to this Agreement shall commence as of
April 5, 1997 (the "Effective Date") and will terminate at the close of business
on April 4, 2000 (the "Termination  Date") unless earlier terminated as provided
herein.

     (b) Executive's employment by the Company hereunder may be terminated prior
to the Termination Date:

          (i) By  Executive  at any time upon the  breach by the  Company of any
     material term of this  Agreement,  provided that Executive  shall have sent
     written  notice of such breach to the Chairman of the Board and the Company
     shall have  failed to correct  such breach  within  thirty (30) days of its
     receipt of such notice;

          (ii) By the Company  immediately  For Cause.  For purposes hereof "For
     Cause"  shall mean (A) any  willful  and  knowing  material  breach of this
     Agreement by Executive; (B) any attempt by Executive to secure any personal
     profit in  connection  with the  business  of the  Company  not  previously
     disclosed  to and  approved  by the  Company and a majority of its Board of
     Directors;  (C) Executive's  criminal  conviction for fraud,  embezzlement,
     bribery or any  felonious  offense;  or (D)  Executive's  commission of any
     willful and intentional act of fraud or dishonesty against the


                                       17


     Company.  In the event the Company terminates  Executive's  employment "For
     Cause" the Board shall provide  Executive as soon as  practicable  (but not
     later than seven (7) business days thereafter)  with a written  explanation
     of the reasons for such termination;

          (iii) By the Company upon Executive's Disability.  For purposes hereof
     "Disability"  shall  mean a physical  or mental  condition  which  prevents
     Executive from  performing his duties  hereunder for a continuous six month
     period or for a total of six months during any 18 month period;

          (iv) Upon the death of Executive; or

          (v) By the Company  upon a unanimous  determination  by the  Company's
     Board of Directors  (other than  Executive if Executive is then a member of
     the Board) that Executive has failed to meet the performance criteria which
     would  reasonably be expected of someone in his position.  In the event the
     Company terminates  Executive's employment based upon such determination by
     the Board,  the Board shall provide  Executive as soon as practicable  (but
     not  later  than  seven  (7)  business  days  thereafter)  with  a  written
     explanation of the facts on which the termination is based.

     (c) Except as otherwise  provided  herein,  upon termination of Executive's
employment hereunder,  the Company shall have no further obligation to Executive
or his  personal  representative  with  respect to  remuneration  due under this
Agreement.


                                       18


     5.   Notices.

     All notices,  requests,  demands and other  communications  provided for by
this  Agreement  shall be in writing and shall be deemed to have been given when
delivered by hand and  acknowledged  by receipt or when mailed at any general or
branch United States Post Office enclosed in a registered or certified  postpaid
envelope and addressed to the address of the respective party stated below or to
such changed address as the party may have fixed by notice:

                  To the Company:   Enzon, Inc.
                                    20 Kingsbridge Road
                                    Piscataway, NJ  08854
                                    Attn: Corporate Secretary

                  To Executive:     Peter Tombros
                                    159 Lambert Road
                                    New Canaan, Connecticut  06840

     6.   Miscellaneous.

     (a) This Agreement shall be construed, interpreted and governed by the laws
of the State of New Jersey,  without  regard to the conflicts of law  provisions
thereof.

     (b) This  Agreement  shall be  binding  upon and  inure to the  benefit  of
Executive,  his  legal  representatives,  heirs and  distributees,  and shall be
binding upon and inure to the benefit of the  Company,  and its  successors  and
assigns;  provided,  however, that, because this Agreement is a personal service
contract, Executive shall not assign any of his employment duties or obligations
hereunder and any purported assignment shall be null and void ab initio.


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     (c)  Except as  otherwise  specifically  provided  herein,  this  Agreement
contains the entire agreement of the parties with respect to its subject matter,
and no waiver,  modification  or change of any of its provisions  shall be valid
unless in writing  and signed by the party  against  whom such  claimed  waiver,
modification or change is sought to be enforced.

     (d) Except as otherwise specifically provided for hereunder,  the waiver of
any breach of any duty,  term or condition of this Agreement shall not be deemed
to constitute a waiver of any  preceding or succeeding  breach of the same or of
any other duty, term or condition of this Agreement.

     (e) The headings of the  sections and  subsections  of this  Agreement  are
inserted  for  convenience  only and shall not be  deemed to  constitute  a part
hereof or to affect the meaning thereof.

     (f) Executive  represents  and warrants that his  performance of all of the
terms of this  Agreement and of his  obligations  as an executive of the Company
does not and will not breach any non-competition  agreement or agreement to keep
in  confidence  any  proprietary  information  or  knowledge  acquired by him in
confidence  or in trust  from a third  party  prior to his  employment  with the
Company.

     (g) Any claim or  controversy  arising out of or relating to this Agreement
or the breach hereof shall be settled by arbitration in accordance with the laws
of the State of New Jersey.  Such arbitration shall be conducted in the State of
New


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Jersey in accordance  with the rules then  existing of the American  Arbitration
Association.  Judgment upon the award rendered by the arbitrators may be entered
in any court having  jurisdiction  thereof.  In the event of any dispute arising
under this Agreement, the prevailing party shall be entitled to reasonable legal
fees and disbursements incurred in connection therewith.


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     (h) Whenever the context  requires,  any pronouns used herein shall include
the corresponding masculine, feminine or neuter forms, and the singular forms of
nouns and pronouns shall include the plural forms and vice versa.

     IN WITNESS WHEREOF,  the parties have executed this Agreement  effective as
of the day and year first above written.

                                        EXECUTIVE

                                        /s/PETER TOMBROS
                                        -------------------------
                                        Peter Tombros

                                        ENZON, INC.

                                        By:/s/JOHN A. CARUSO
                                           -----------------------
                                           John A. Caruso
                                           Vice President, Business
                                           Development, General Counsel


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