ENZON, INC.

                                4,000,000 Shares

                          Common Stock, $0.01 Par Value

                            PLACEMENT AGENT AGREEMENT


                                  June 25, 1998


SBC Warburg Dillon Read Inc.
535 Madison Avenue
New York, New York  10022

Ladies and Gentlemen:

     The  undersigned,  Enzon,  Inc., a Delaware  corporation  (the  "Company"),
hereby confirms its agreements with SBC Warburg Dillon Read Inc. (the "Placement
Agent") as follows:

     1.  Description  of the Shares.  The Company has  authorized by appropriate
corporate  action  and  proposes  to sell  in the  manner  contemplated  by this
Placement  Agent  Agreement  (the  "Agreement")  up  to  4,000,000  shares  (the
"Shares") of its Common Stock, $0.01 par value (the "Common Stock").

     2.  Closing.  The  closing  of the  purchase  and sale of the Shares to the
Purchasers  (as such  term is  defined  in the  form of  Common  Stock  Purchase
Agreement  attached  as Appendix A to the  Offering  Memorandum  (the  "Purchase
Agreement")),  pursuant to the Purchase  Agreement (the "Closing") shall be held
at the offices of Dorsey & Whitney  LLP,  250 Park  Avenue,  New York,  New York
10177 at or before 10:00 a.m.,  New York time,  on the date that is two business
days after the date on which the Registration Statement on Form S-3 contemplated
by the Purchase Agreement  (including all amendments thereto,  the "Registration
Statement") is declared effective or at such other time and place as the Company
and the Placement  Agent may agree (the  "Closing  Date").  At the Closing,  the
Purchasers  shall  deliver to the  Placement  Agent wire  transfers in the gross
amount due to the Company for the Shares being  purchased by each  Purchaser and
the  Placement  Agent shall  deliver to the  Company a wire  transfer in the net
amount due to the Company (after deducting the Placement Agent Fee (as





defined in Section  4(b) for such  Shares to the extent (and only to the extent)
that payments have been  delivered to the Placement  Agent by the Purchasers for
such Shares (it being understood that the Company will not be obligated to issue
any  Shares  for which full  payment  of the gross  purchase  price has not been
received).

     3.  Representations  and Warranties of the Company.  The Company represents
and warrants to and agrees with the Placement Agent that:

          (a) The  Private  Placement  Offering  Memorandum  dated  June 4, 1998
     (including  appendices  thereto,   information  incorporated  by  reference
     therein and the  financial  statements of the Company and the related notes
     thereto  included  therein),  as  amended  and  supplemented  prior  to the
     execution  hereof,  and all amendments and supplements  thereto  (including
     appendices thereto,  information  incorporated by reference therein and the
     financial  statements of the Company and the related notes thereto included
     therein)  delivered to the Purchasers  prior to the Closing  (collectively,
     the "Offering  Memorandum") at the date hereof does not, and at the Closing
     will not,  contain any untrue statement of a material fact or omit to state
     a material  fact  required to be stated  therein or  necessary  to make any
     statements  therein, in the light of the circumstances under which they are
     made, not misleading;  provided,  however, that none of the representations
     and warranties  contained in this  subparagraph  shall apply to information
     that relates to the plan of  distribution or to the Placement Agent that is
     included in the Offering  Memorandum  in reliance  upon,  and in conformity
     with, written  information  furnished to the Company by the Placement Agent
     specifically for inclusion therein.

          (b) The Company has filed all the  documents  (collectively,  the "SEC
     Documents")  that the Company was required to file with the  Securities and
     Exchange Commission (the "Commission") under Section 13, 14 or 15(d) of the
     Securities and Exchange Act of 1934, as amended (the "Exchange  Act") since
     the effective date of the registration  statement filed with respect to its
     initial public offering.  The SEC Documents,  when they were filed with the
     Commission,  conformed in all material  respects to the requirements of the
     Securities  Act of 1933,  as amended  (the "Act") or the  Exchange  Act, as
     applicable,  and the rules,  regulations and instructions of the Commission
     thereunder,  and any  documents  so filed and included or  incorporated  by
     reference  in  the  Offering  Memorandum  or  the  Registration   Statement
     subsequent  to  the  date  hereof  will,  when  they  are  filed  with  the
     Commission,  conform in all material  respects to the  requirements  of the
     Exchange Act and the rules,  regulations and instructions of the Commission
     thereunder;  and when such documents were or are filed with the Commission,
     none of such documents  included or will include any untrue  statement of a
     material  fact or omitted or will omit to state any material  fact required
     to be stated  therein or necessary to make the statements  therein,  in the
     light of the circumstances under which they were made, not misleading.

          (c) The Company has been duly  incorporated and is validly existing as
     a  corporation  in good  standing  under  the laws of its  jurisdiction  of
     incorporation  with full power and authority  (corporate and other) to own,
     lease and operate its properties and conduct its


                                       2



     business as described in the  Offering  Memorandum;  except as described in
     Schedule  3(c)  hereto,  the Company  does not own or control,  directly or
     indirectly any  corporation,  association  or other entity;  the Company is
     duly  qualified  to do  business  as a foreign  corporation  and is in good
     standing  in each  jurisdiction  in  which  the  ownership  or  leasing  of
     properties  or the conduct of its  business  requires  such  qualification,
     except  where the  failure  to be so  qualified  would not have a  material
     adverse  effect  on  the  condition  (financial  or  otherwise),  earnings,
     operations,  business  or business  prospects  of the  Company;  except for
     product   marketing   approvals   by  the  United   States  Food  and  Drug
     Administration and comparable foreign regulatory  agencies described in the
     Offering Memorandum required for the conduct of its business as proposed to
     be conducted in the future,  the Company is in  possession of and operating
     in compliance with all authorizations,  licenses,  certificates,  consents,
     orders and permits  from state,  federal and other  regulatory  authorities
     which are applicable to the conduct of its business as presently  conducted
     and proposed to be conducted,  all of which are valid and in full force and
     effect, except where the failure to so possess or so operate would not have
     a  material  adverse  effect on the  condition  (financial  or  otherwise),
     earnings,  operations,  business or business prospects of the Company;  the
     Company  is not in  violation  of its  respective  charter  or bylaws or in
     breach or default (nor has any event occurred  which with notice,  lapse of
     time, or both,  would constitute a breach or default) in the performance or
     observance  of any material  obligation,  agreement,  covenant or condition
     contained  in any  material  bond,  debenture,  note or other  evidence  of
     indebtedness  or  in  any  material  contract,  indenture,  mortgage,  loan
     agreement,  joint  venture or other  agreement or  instrument  to which the
     Company is a party or by which it or any of its  properties may be bound or
     in material violation of any law, order, rule, regulation, writ, injunction
     or decree of any government,  government instrumentality or court, domestic
     or foreign,  of which it has  knowledge,  except for violations or defaults
     which are not material to the Company.

          (d) The Company has full legal  right,  power and  authority  to enter
     into this  Agreement  with the  Placement  Agent and to enter into a Common
     Stock Purchase Agreement,  a form of which is attached as Appendix A to the
     Offering  Memorandum,  with each purchaser (a  "Purchaser")  of Shares (the
     "Purchase Agreement"),  and to perform the transactions contemplated hereby
     and  thereby.  This  Agreement  and the Purchase  Agreement  have been duly
     authorized,  executed and delivered by the Company,  and this Agreement and
     the Purchase Agreement,  upon their execution,  delivery and performance by
     the Company (assuming due execution,  delivery and performance by the other
     parties thereto),  will be valid and binding  agreements on the part of the
     Company,  enforceable in accordance  with their terms,  except as rights to
     indemnity  and  contribution  hereunder  and  thereunder  may be limited by
     applicable  law and except as the  enforcement  hereof and  thereof  may be
     limited by applicable bankruptcy, insolvency, reorganization, moratorium or
     other similar laws affecting  creditors'  rights  generally,  or by general
     equitable  principles;  the  performance of this Agreement and the Purchase
     Agreement  and the  consummation  of the  transactions  herein and  therein
     contemplated  will not result in a breach or  violation of any of the terms
     and  provisions  of, or  constitute  a default  under,  (i) any  indenture,
     mortgage, deed of trust, loan agreement, bond, debenture, note agreement or
     other evidence of  indebtedness,  or any material lease,  contract or other
     agreement


                                       3



     or  instrument  to which the Company is a party or by which the property of
     the  Company is bound,  or (ii) the  charter or bylaws of the  Company,  or
     (iii) any law,  order,  rule,  regulation,  writ,  injunction,  judgment or
     decree of any court or governmental agency or body having jurisdiction over
     the  Company  or  over  the  properties  of the  Company;  and no  consent,
     approval,  authorization  or order of any court or  governmental  agency or
     body is required for the  consummation  by the Company of the  transactions
     herein  contemplated,  except  such as may be required  under the Act,  the
     Exchange Act or under state or other securities or Blue Sky laws.

          (e) There is not any  pending  or, to the  knowledge  of the  Company,
     threatened any action, suit, claim or proceeding against the Company or any
     of its  respective  officers or any of their  properties,  assets or rights
     before  any court or  governmental  agency or body or  otherwise  which (i)
     might result in any material adverse change in the condition  (financial or
     otherwise),  earnings,  operations,  business or business  prospects of the
     Company or might materially and adversely affect its properties,  assets or
     rights or (ii) might prevent consummation of the transactions  contemplated
     hereby which have not been accurately described in all material respects in
     the Offering Memorandum.

          (f) All  outstanding  shares of capital stock of the Company have been
     duly  authorized and validly  issued and are fully paid and  nonassessable,
     have been issued in compliance with all federal and state  securities laws,
     were not issued in  violation  of or subject  to any  preemptive  rights or
     other rights to subscribe for or purchase  securities,  and the  authorized
     and outstanding capital stock of the Company conforms,  as of the dates for
     which such information is given, in all material respects to the statements
     relating thereto contained in Exhibit G to the Purchase Agreement; there is
     no capital  stock  outstanding  as of such dates other than as described in
     Exhibit G to the Purchase Agreement;  and all issued and outstanding shares
     of capital  stock of the  Company  have been duly  authorized  and  validly
     issued and are fully paid and nonassessable.

          (g) Except as disclosed in or contemplated by the Offering Memorandum,
     the  Company  does not have  outstanding  any options to  purchase,  or any
     preemptive  rights or other  rights to subscribe  for or to  purchase,  any
     securities or obligations convertible into, or any contracts or commitments
     to issue or sell, shares of its capital stock or any such options,  rights,
     convertible securities or obligations. No stockholder of the Company, other
     than the  Purchasers,  has any right  (which has not been waived or has not
     expired by reason of lapse of time following  notification of the Company's
     intent to file the  Registration  Statement)  to  require  the  Company  to
     register the sale of any shares owned by such stockholder  under the Act in
     the Registration  Statement,  except  stockholders of the Company with such
     rights that are  eligible to sell all of such  securities  pursuant to Rule
     144(k) promulgated under the Act.

          (h) The  Shares  have been  duly  authorized,  and,  when  issued  and
     delivered  pursuant to the Purchase  Agreement,  will have been duly issued
     and delivered;  and the Shares will conform to the  description  thereof in
     Exhibit G to the Purchase Agreement in all material respects.


                                       4



          (i) Except as disclosed in the Offering  Memorandum,  the Company owns
     or possesses sufficient rights to use all existing patents,  patent rights,
     inventions, trade secrets, know-how,  proprietary rights and processes that
     are  necessary  for the conduct  and  proposed  conduct of its  business as
     described in the Offering Memorandum (the "Company's  Proprietary  Rights")
     without any  conflict  with or  infringement  of the rights of others which
     would result in a material  adverse  effect on the condition  (financial or
     otherwise),  earnings,  operations,  business or business  prospects of the
     Company.  The Company  believes that there are no third parties who have or
     will  be able  to  establish  rights  to any of the  Company's  Proprietary
     Rights, except for (i) the ownership rights of the third party licensors to
     the Company's  Proprietary Rights which are licensed to the Company by such
     third party  licensors and (ii) the third party  licensees of the Company's
     Proprietary Rights. Except as disclosed in the Offering Memorandum,  to the
     knowledge of the Company,  there is no infringement by any third parties of
     any of  the  Company's  Proprietary  Rights.  Except  as  disclosed  in the
     Offering Memorandum, the Company has not received any notice of, and has no
     knowledge of any basis for, any  infringement  of or conflict with asserted
     rights of others with respect to any patent, patent right, invention, trade
     secret,  know-how or other proprietary rights that,  individually or in the
     aggregate, would have a material adverse effect on the condition (financial
     or otherwise),  earnings, operations, business or business prospects of the
     Company.

          (j) While there can be no  assurance  that FDA approval for any of the
     Company's  products  will be obtained  on a timely  basis,  or at all,  the
     Company  has  received no  communication  from the FDA  expressing  adverse
     comments, questions or concerns with regard to (i) any New Drug Application
     filed by the  Company  or (ii)  any  current  or  pending  clinical  trials
     relating to any of the Company's products,  other than comments,  questions
     or concerns to which the Company reasonably  believes it has responded,  or
     can respond,  to the satisfaction of the FDA without  unreasonable delay or
     expense and without  materially  impairing the  commercial  feasibility  of
     introducing  the  product in  question.  The  Company  has  applied for and
     obtained  from  the FDA an  Investigational  New  Drug  exemption  for each
     product with respect to which it has commenced human clinical  trials,  and
     all such  human  clinical  trials are being  conducted,  to the best of the
     Company's  knowledge,  in  compliance  in all  material  respects  with the
     protocols  submitted by the Company to the FDA and any conditions  relating
     thereto  imposed by the FDA.  The Company  has  received no notice from the
     FDA, and has no reason to believe,  that its  manufacturing  facilities  or
     processes are not in compliance  with current good  manufacturing  practice
     requirements.

          (k)  KPMG  Peat  Marwick  LLP,   which  has  examined  the   financial
     statements,  together with the related  schedules and notes, of the Company
     as of June  30,  1995,  1996 and 1997 and for the  years  then  ended,  are
     independent  accountants  within  the  meaning of the Act and the rules and
     regulations promulgated by the Commission thereunder; the audited financial
     statements of the Company,  together with the related  schedules and notes,
     and the  unaudited  financial  information  forming  part  of the  Offering
     Memorandum  fairly  present  the  financial  position  and the  results  of
     operations of the Company at the  respective  dates and for the  respective
     periods to which they apply; and all audited financial statements, together
     with the


                                       5



     related schedules and notes, and the unaudited financial information,  have
     been prepared in accordance with generally accepted  accounting  principles
     consistently  applied  throughout  the  periods  involved  except as may be
     otherwise stated therein;  provided,  however, that the unaudited financial
     statements are subject to normal recurring year-end adjustments (which will
     in any case not be  material)  and do not  contain all  footnotes  required
     under generally  accepted  accounting  principles).  The selected financial
     data included in the Offering  Memorandum  present  fairly the  information
     shown therein and have been compiled on a basis consistent with the audited
     financial statements referred to above.

          (l) Except as described in the Offering Memorandum,  subsequent to the
     respective  dates  as  of  which  information  is  given  in  the  Offering
     Memorandum  through the date  hereof,  there has not been (i) any  material
     adverse change in the business,  properties or assets described or referred
     to in the  Offering  Memorandum,  or the results of  operations,  condition
     (financial  or  otherwise)  earnings,  operations,   business  or  business
     prospects,  of the Company,  (ii) any  transaction  that is material to the
     Company,  except transactions in the ordinary course of business and except
     as described  in the  Offering  Memorandum,  (iii) any  obligation  that is
     material to the  Company,  direct or  contingent,  incurred by the Company,
     except  obligations  incurred in the ordinary course of business,  (iv) any
     change in the capital  stock or  outstanding  indebtedness  of the Company,
     which is material to the Company,  except for the exercise of stock options
     disclosed as  outstanding,  or (v) any dividend or distribution of any kind
     declared, paid or made on the capital stock of the Company.

          (m) Except as set forth in the  Offering  Memorandum,  (i) the Company
     has good  and  marketable  title  to all  properties  and  material  assets
     described in the Offering  Memorandum as owned by it, free and clear of any
     pledge, lien, security interest,  encumbrance,  claim or equitable interest
     other than such as are not material to the  business of the  Company,  (ii)
     the  agreements  to which the Company is a party  described in the Offering
     Memorandum  are valid  agreements in full force and effect,  enforceable by
     the Company, except as the enforcement thereof may be limited by applicable
     bankruptcy,  insolvency,  reorganization,  moratorium or other similar laws
     affecting  creditors' rights generally or by general  equitable  principles
     and,  to the  knowledge  of the  Company,  the other  contracting  party or
     parties thereto are not in material breach or material default under any of
     such agreements, and (iii) the Company has valid and enforceable leases for
     the  properties  described in the Offering  Memorandum as leased by it with
     such  exceptions as are not material,  except as enforcement may be limited
     by applicable bankruptcy, insolvency,  reorganization,  moratorium or other
     similar laws  relating to or affecting  creditors'  rights  generally or by
     general equitable principles.

          (n) Except as disclosed in the Offering Memorandum, (i) the Company is
     in  compliance  in  all  material   respects  with  all  rules,   laws  and
     regulations, and has all necessary permits, relating to the use, treatment,
     storage and disposal of toxic  substances  and  protection of health or the
     environment  ("Environmental  Laws") which are  applicable to its business,
     (ii)  the  Company  has not  received  any  notice  from  any  governmental
     authority  or third party of an asserted  claim under  Environmental  Laws,
     (iii) to the knowledge of the Company, no facts


                                        6



     currently  exist that will  require  the  Company to make  future  material
     capital  expenditures  to comply with  Environmental  Laws, and (iv) to the
     knowledge of the Company, no property which is or has been owned, leased or
     occupied by the Company has been designated as a Superfund site pursuant to
     the Comprehensive Environmental Response, Compensation and Liability Act of
     1980, as amended (42 U.S.C. ss. 9601, et seq.), or otherwise  designated as
     a contaminated site under applicable state or local law.

          (o) The Company has filed all  necessary  federal and state income and
     franchise  tax  returns  and has paid all taxes  due,  and there are no tax
     payment  or  filing  deficiencies  that  have  been  or,  to the  Company's
     knowledge, might be asserted against the Company that might have a material
     adverse  effect  on  the  condition  (financial  or  otherwise),  earnings,
     operations, business or business prospects of the Company considered as one
     enterprise; all tax liabilities are adequately provided for on the books of
     the Company, in all material respects.

          (p) The Company  maintains  insurance  of the types and in the amounts
     generally deemed adequate for its business,  including  without  limitation
     insurance  covering  real and  personal  property  owned or  leased  by the
     Company against theft, damage,  destruction,  acts of vandalism and, to the
     best of the  Company's  knowledge,  all  other  risks  customarily  insured
     against, all of which insurance is in full force and effect.

          (q) To the  knowledge  of the  Company,  no labor  disturbance  by the
     employees of the Company  exists or is imminent;  no collective  bargaining
     agreement exists with any of the Company's  employees and, to the knowledge
     of the Company, no such agreement is imminent.

          (r) The  Company has not been  advised,  and has no reason to believe,
     that it is not  conducting  business  in  compliance  with all of the laws,
     rules  and  regulations  of the  jurisdictions  in which  it is  conducting
     business  except  where  failure  to be so in  compliance  would not have a
     material  adverse  effect  on  the  condition   (financial  or  otherwise),
     earnings, operations, business or business prospects of the Company.

          (s) The Company has not distributed  and will not distribute  prior to
     the Closing Date or on any date on which Shares are to be purchased, as the
     case may be, any offering material in connection with the offering and sale
     of the Shares other than the Offering Memorandum.

          (t) The  Company  has not at any time  during  the last five years (i)
     made any unlawful  contribution  to any  candidate for foreign  office,  or
     failed to disclose fully any contribution in violation of law, or (ii) made
     any payment to any federal or state  governmental  officer or official,  or
     other person charged with similar public or quasi-public duties, other than
     payments  required  or  permitted  by the laws of the United  States of any
     jurisdiction thereof.


                                       7



          (u) The  Company  has  not  taken  and  will  not  take,  directly  or
     indirectly,  any action  designed to, or that might be reasonably  expected
     to, cause or result in  stabilization  or  manipulation of the price of the
     Shares to facilitate the sale or resale of the Shares.

          (v) The Company is not an "investment  company"  within the meaning of
     the Investment Company Act of 1940, as amended.

     4. Appointment of Placement Agent; Agreements of Placement Agent.

          (a) Subject to the terms and conditions stated in this Agreement,  the
     Company  hereby  appoints the Placement  Agent its placement  agent for the
     purpose  of  offering  and  selling  the Shares in a private  placement  to
     "accredited investors" as defined in Rule 501(a) under the Act.

          (b) In connection with the offers and sales of the Shares, the Company
     will pay the  Placement  Agent a  placement  agent fee for its  services in
     acting as Placement  Agent for the Company in the sale of the Shares in the
     amount of $900,000,  provided  that in no event shall such fee exceed 6% of
     the  gross  proceeds  to the  Company  from  the  sale of the  Shares  (the
     "Placement Agent Fee").

          (c) The Placement  Agent will use diligent  efforts to sell the Shares
     on  behalf  of the  Company  at the price and on the terms set forth in the
     Offering Memorandum and the Purchase Agreement; provided, however, that the
     Company  understands  that the  Placement  Agent has no  obligation to find
     Purchasers.  The  Placement  Agent  will use  diligent  efforts  to  obtain
     performance  by  each  Purchaser,  but the  Placement  Agent  will  have no
     liability to the Company in the event any such purchase is not  consummated
     for any reason not related to the gross negligence or willful misconduct of
     the Placement  Agent. The Company also understands that the Placement Agent
     is under no obligation to purchase any Shares for its own account. While it
     is  contemplated   that  the  Placement  Agent  may  purchase  Shares  from
     Purchasers and resell such Shares in its capacity as a market-maker  or may
     act as agent  in the  resale  of  Shares  in  brokerage  transactions,  the
     Placement  Agent shall not act as an underwriter in connection with resales
     of the  Shares  or  participate  in any other  way in the  drafting  of the
     Registration Statement or the resale of the Shares.

          (d) The Placement  Agent agrees that in carrying out the  transactions
     contemplated by this Agreement, it has observed and will observe and comply
     with (i) all applicable securities laws, regulations,  rules and ordinances
     in any jurisdiction in which the Shares may be offered,  sold or delivered,
     including, without limitation, Rule 502 and Rule 506 under the Act and (ii)
     all  applicable  regulations  and  rules  of the  National  Association  of
     Securities Dealers,  Inc.; provided,  however,  that except as specifically
     provided  herein,  the Placement  Agent assumes no  responsibility  for the
     accuracy  or  completeness   of  information   contained  in  the  Offering
     Memorandum or provided to Purchasers  in connection  with their  investment
     decisions.


                                        8



          (e) The  Placement  Agent agrees that (i) it will deliver the Offering
     Memorandum  to all  purchasers  prior to their  execution  of the  Purchase
     Agreement,  (ii) it will not deliver the Offering  Memorandum to any person
     that it does not reasonably  believe to be an "accredited  investor"  under
     Section 501(a) of the Act, (iii) promptly upon receipt of a notice pursuant
     to Section 5(d) hereto, it shall suspend offers for sale, and solicitations
     of purchases,  of the Shares and cease using the Offering  Memorandum until
     such time as the  Company  advises the  Placement  Agent that it may resume
     offers for sale, and solicitations of purchases,  of the Shares and (vi) it
     will not  deliver any  materials  regarding  the Company to the  purchasers
     other than the Offering Memorandum.

          (f) The Company will pay all  expenses,  fees and taxes in  connection
     with (i) the  preparation  and  printing and  reproducing  of copies of the
     Offering Memorandum and all amendments and supplements  thereto,  including
     in each case all  documents  incorporated  by reference  therein,  and this
     Agreement,  (ii) the delivery of the Shares,  (iii) the  qualification  for
     offer and sale of the Shares under securities laws as aforesaid  (including
     filing fees and reasonable fees and  disbursements of the Placement Agent's
     counsel in connection  therewith) and all registrations and listings of the
     Shares,  (iv) the furnishing of the opinions of counsel for the Company and
     other certificates referred to herein, (v) travel and related expenses with
     respect to Company  personnel in connection  with any road show and (vi) up
     to $50,000 of the expenses of the Placement  Agent in  connection  with the
     sale of the  Shares,  including  expenses  related to visits to the Company
     with  prospective  Purchasers  or any road show  expenses of the  Placement
     Agent and the reasonable  fees and costs of counsel for the Placement Agent
     in connection with the transactions  contemplated hereby or by the Purchase
     Agreement.

     5. Agreements of the Company. The Company agrees:

          (a) to use its best  efforts to qualify  the Shares for offer and sale
     as  contemplated  hereby in such  jurisdictions  as the Placement Agent may
     reasonably  designate and to continue such  qualifications in effect for so
     long as may be required in connection with the sale of the Shares; provided
     that the Company shall not be required to qualify as a foreign  corporation
     or dealer in securities or to a general consent to service of process or to
     file an annual report in any jurisdiction;

          (b) to  deliver  to the  Placement  Agent  without  charge  as soon as
     practicable  after each  supplement  to the Offering  Memorandum or amended
     Offering  Memorandum  has been  prepared,  as many  copies of the  Offering
     Memorandum  as then  amended or  supplemented  as the  Placement  Agent may
     reasonably  request  for  the  purposes  contemplated  by the  Act or  this
     Agreement;

          (c) to advise the Placement Agent promptly  (confirming such advice in
     writing)  of any  request  made by the  Commission  for  amendments  to any
     document  included or incorporated by reference in the Offering  Memorandum
     or the Registration Statement, or of the


                                        9



     initiation  or  threatened  initiation  of  proceedings  for the purpose of
     entering a stop order with  respect to the  Registration  Statement  or for
     additional information with respect to any thereof;

          (d) for so long as sales  pursuant to this  Agreement and the Purchase
     Agreement are  continuing  and either (i) any event shall occur as a result
     of which the Offering  Memorandum  would include any untrue  statement of a
     material fact or omit to state any material fact necessary in order to make
     the statements  therein, in the light of the circumstances under which they
     were made,  when such Offering  Memorandum is delivered,  not misleading or
     (ii) for any other reason it shall be necessary to amend or supplement  the
     Offering  Memorandum  or to  file  under  the  Exchange  Act  any  document
     incorporated  by reference in the  Offering  Memorandum  in order to comply
     with the Act or the Exchange Act, to notify the Placement Agent promptly to
     suspend offers for sale and  solicitations of purchases of the Shares;  the
     Placement  Agent agrees that promptly  after the receipt of such notice the
     Placement Agent will suspend offers for sale and solicitations of purchases
     of the Shares and cease using the Offering  Memorandum;  and if the Company
     shall  determine so to amend or  supplement  the Offering  Memorandum or to
     file such  document  under the Exchange Act, the Company will so advise the
     Placement Agent and will promptly prepare an amendment or supplement to the
     Offering Memorandum or a document as required by the Exchange Act and will,
     in the case of a  document  required  under  the  Exchange  Act,  file such
     document with the  Commission  that will correct such statement or omission
     or effect such  compliance and will advise the Placement  Agent when it may
     resume offers for sale, and solicitations of purchases, of the Shares.

     6.  Conditions to Placement  Agent's  Obligations.  The  obligations of the
Placement Agent hereunder shall be subject, in its discretion,  to the following
conditions:

          (a)  All  representations,  warranties  and  other  statements  of the
     Company shall be at the Closing true and correct in all material respects.

          (b) The Company  shall have  performed  in all  material  respects its
     obligations hereunder.

          (c) No court or  administrative  order  prohibiting  the Closing shall
     have been issued and no  proceedings  for that purpose  shall be pending or
     threatened.

          (d) All  corporate  proceedings  and other legal matters in connection
     with this Agreement,  the Purchase  Agreement,  the Offering Memorandum and
     the  authorization,  issue, sale and delivery of the Shares shall have been
     reasonably satisfactory to counsel for the Placement Agent, and the Company
     shall have furnished to counsel for the Placement  Agent such documents and
     information  as it may have  requested  for the  purpose  of  enabling  the
     Placement Agent to pass upon the legal matters referred to above.


                                       10



          (e) The  Placement  Agent shall have  received  an opinion  reasonably
     satisfactory  to the  Placement  Agent,  dated as of the Closing  Date,  of
     Dorsey & Whitney LLP, counsel to the Company,  substantially in the form of
     Exhibit A to this Agreement.

          (f) The  Placement  Agent shall have  received  an opinion  reasonably
     satisfactory  to the  Placement  Agent,  dated as of the Closing  Date,  of
     patent  counsel to the  Company,  with  respect to the matters set forth on
     Exhibit D to the Purchase Agreement.

          (g) The Company shall have furnished the Placement Agent a certificate
     of the Company,  dated as of the Closing Date and executed by the President
     of the Company,  stating that,  since the date as of which  information  is
     given in the  Offering  Memorandum,  (i) the Company has not  incurred  any
     liabilities or obligations,  contingent or otherwise,  that are material in
     the  aggregate  to the  Company,  taken as a whole,  except in the ordinary
     course of business,  (ii) there has been no material  adverse change in the
     condition or results of operations, financial or otherwise, of the Company;
     (iii)  there has been no document  required to be filed under the  Exchange
     Act and the rules and  regulations  thereunder  that has not been so filed,
     (iv) no order  preventing the Closing is in effect and no  proceedings  for
     that  purpose  are pending or  threatened  by the  Commission,  and (v) all
     representations  and  warranties  of the Company  herein are true as of the
     Closing.

          (h) The Registration Statement registering the resale of the Shares by
     the  Purchasers  shall have been filed with and  declared  effective by the
     Commission,  and no stop order suspending the effectiveness  thereof and no
     proceedings therefor shall be pending or threatened by the Commission.

          (i) Prior to the Closing Date, the shares to be issued and sold by the
     Company  shall have been duly  authorized  for listing by the Nasdaq  Stock
     Market.

          (j) The Company shall have furnished to the Placement Agent such other
     affidavits  and  certificates  as to the accuracy and  completeness  of any
     statement in the Offering  Memorandum  as of the Closing Date and as to any
     other matter in connection with the transactions  contemplated hereby or by
     the Purchase Agreement as the Placement Agent may reasonably request.

     All opinions, letters, certificates and affidavits above mentioned shall be
deemed to be in compliance with this Section 6 only if they shall be in form and
substance reasonably satisfactory to counsel for the Placement Agent.

     In case any of the conditions  specified  above in this Section 6 shall not
have been  fulfilled,  the  Placement  Agent shall have no obligation to proceed
with any offer for sale, or any solicitation of purchases, of the Shares.


                                       11



     7. Indemnification.

          (a) The Company  agrees to  indemnify,  defend and hold  harmless  the
     Placement  Agent and any person who controls the Placement Agent within the
     meaning of Section  15 of the Act or  Section 20 of the  Exchange  Act (the
     "Placement  Agent  Affiliates"),   from  and  against  any  loss,  expense,
     liability or claim (including the reasonable cost of investigation)  which,
     jointly or  severally,  any such  Placement  Agent  Affiliates  controlling
     person may incur insofar as such loss,  expense,  liability or claim arises
     out of or is based upon any untrue statement or alleged untrue statement of
     a material  fact  contained  in the  Offering  Memorandum  or  Registration
     Statement,  or  arises  out of or is based  upon any  omission  or  alleged
     omission  to state a material  fact  required  to be stated in either  such
     Offering  Memorandum  or  Registration  Statement  necessary  to  make  the
     statements  made therein not  misleading,  except insofar as any such loss,
     expense,  liability  or claim  arises  out of or is based  upon any  untrue
     statement or alleged  untrue  statement of a material fact contained in and
     in conformity with information  furnished in writing by the Placement Agent
     or any Placement  Agent  Affiliates  to the Company  expressly for use with
     reference  to  such  Placement   Agent  in  such  Offering   Memorandum  or
     Registration Statement.

          If any action is brought  against  the  Placement  Agent or  Placement
     Agent  Affiliate in respect of which  indemnity  may be sought  against the
     Company  pursuant to the foregoing  paragraph,  the  Placement  Agent shall
     promptly  notify the Company in writing of the  institution  of such action
     and the Company  shall  assume the defense of such  action,  including  the
     employment of counsel and payment of expenses.  Such Placement Agent or any
     Placement  Agent  Affiliate shall have the right to employ its or their own
     counsel  in  any  such  case,   such  counsel  which  shall  be  reasonably
     satisfactory  to the  Company,  but the fees and  expenses of such  counsel
     shall be at the  expense of such  Placement  Agent or any  Placement  Agent
     Affiliate  unless the employment of such counsel shall have been authorized
     in writing by the Company in connection  with the defense of such action or
     the Company shall not have  employed  counsel to have charge of the defense
     of such action or such  indemnified  party or the  Placement  Agent or such
     Placement Agent Affiliate shall have reasonably concluded that there may be
     defenses  available to it or them which are different from or additional to
     those  available  to the Company (in which case the Company  shall not have
     the right to direct the defense of such action on behalf of the indemnified
     party or parties), in any of which events such reasonable fees and expenses
     shall be borne by the Company and paid as  incurred  (it being  understood,
     however, that the Company shall not be liable for the expenses of more than
     one separate  counsel in any one action or series of related actions in the
     same jurisdiction  representing the indemnified  parties who are parties to
     such action).  Anything in this paragraph to the contrary  notwithstanding,
     the  Company  shall not be liable for any  settlement  of any such claim or
     action effected without its written consent.

          (b) The Placement Agent agrees to indemnify,  defend and hold harmless
     the Company,  its directors  and officers,  and any person who controls the
     Company  within  the  meaning of Section 15 of the Act or Section 20 of the
     Exchange Act (the "Company Affiliates") 


                                       12



     from and against  any loss,  expense,  liability  or claim  (including  the
     reasonable cost of investigation) which, jointly or severally,  the Company
     or any Company Affiliate may incur insofar as such loss, expense, liability
     or claim (i) arises out of or is based upon any untrue statement or alleged
     untrue  statement of a material fact  contained in and in  conformity  with
     information  furnished in writing by or on behalf of the Placement Agent to
     the Company  expressly for use with reference to the Placement Agent in the
     Offering Memorandum or Registration  Statement, or (ii) arises out of or is
     based upon the gross  negligence  or willful  misconduct  of the  Placement
     Agent with respect to this Agreement as determined in a final judgment by a
     Court of  competent  jurisdiction  from which no appeal can be or is taken.
     Neither the Placement  Agent nor any Placement  Agent  Affiliate shall have
     any liability (whether direct or indirect,  by statute, in contract or tort
     or otherwise)  to the Company or to any third party in connection  with the
     Registration Statement or the resale by the Purchasers of the Shares.

          If any action is brought against the Company or the Company Affiliates
     or any such person in respect of which  indemnity may be sought against the
     Placement  Agent pursuant to the foregoing  paragraph,  the Company or such
     Company  Affiliate  shall promptly notify the Placement Agent in writing of
     the  institution  of such action and the  Placement  Agent shall assume the
     defense of such action,  including the employment of counsel and payment of
     expenses.  The Company or such  Company  Affiliate  shall have the right to
     employ its own counsel in any such case,  but the fees and expenses of such
     counsel  shall be at the expense of the Company or such  Company  Affiliate
     unless (i) the  employment  of such counsel  shall have been  authorized in
     writing  by the  Placement  Agent in  connection  with the  defense of such
     action, (ii) or the Placement Agent shall not have employed counsel to have
     charge of the defense of such action,  (iii) or such  indemnified  party or
     the Company or such Company Affiliates shall have reasonably concluded that
     there may be defenses  available to it or them which are different  from or
     additional  to those  available to the  Placement  Agent (in which case the
     Placement  Agent  shall not have the right to direct  the  defense  of such
     action on  behalf of the  indemnified  party or  parties),  in any of which
     events such  reasonable  fees and expenses  shall be borne by the Placement
     Agent  and  paid as  incurred  (it  being  understood,  however,  that  the
     Placement  Agent  shall not be  liable  for the  expenses  of more than one
     separate counsel in any one action or series of related actions in the same
     jurisdiction  representing the indemnified  parties who are parties to such
     action).  Anything in this paragraph to the contrary  notwithstanding,  the
     Placement Agent shall not be liable for any settlement of any such claim or
     action effected without the written consent of the Placement Agent.

          (c)  If  the  indemnification  provided  for  in  this  Section  7  is
     unavailable to an indemnified  party under  subsections (a) and (b) of this
     Section 7 with  respect  of any  losses,  expenses,  liabilities  or claims
     referred to therein,  then each applicable  indemnifying  party, in lieu of
     indemnifying such indemnified party, shall contribute to the amount paid or
     payable by such  indemnified  party as a result of such  losses,  expenses,
     liabilities  or claims (i) in such  proportion as is appropriate to reflect
     the  relative  benefits  received  by the  Company  on the one hand and the
     Placement  Agent on the other hand from the  offering of the Shares or (ii)
     if the  allocation  provided  by  clause  (i)  above  is not  permitted  by
     applicable law, in such proportion


                                       13



     as is appropriate to reflect not only the relative  benefits referred to in
     clause (i) above but also the relative fault of the Company on the one hand
     and of the Placement  Agent on the other in connection  with the statements
     or  omissions  which  resulted in such  losses,  expenses,  liabilities  or
     claims,  as  well  as any  other  relevant  equitable  considerations.  The
     relative benefits received by the Company on the one hand and the Placement
     Agent on the  other  shall be deemed  to be in the same  proportion  as the
     total proceeds from the offering (net of the Placement Agent Fee but before
     deducting  expenses)  received by the Company bear to the  Placement  Agent
     Fee. The relative fault of the Company on the one hand and of the Placement
     Agent on the other shall be determined by reference to, among other things,
     whether the untrue statement or alleged untrue statement of a material fact
     or  omission or alleged  omission  relates to  information  supplied by the
     Company  or by the  Placement  Agent  and  the  parties'  relative  intent,
     knowledge, access to information and opportunity to correct or prevent such
     statement or omission. The amount paid or payable by a party as a result of
     the losses,  expenses,  liabilities  and claims  referred to above shall be
     deemed to include any legal or other fees or expenses  reasonably  incurred
     by such party in connection  with  investigating  or defending any claim or
     action. 

          (d) The  Company  and the  Placement  Agent agree that it would not be
     just  and  equitable  if  contribution  pursuant  to  this  Section  7 were
     determined by pro rata allocation or by any other method of allocation that
     does  not take  account  of the  equitable  considerations  referred  to in
     subsection (c) above. Notwithstanding the provisions of this Section 7, the
     Placement Agent shall not be required to contribute any amount in excess of
     the amount by which the total price at which the Shares  were sold  exceeds
     the amount of any damages  which the  Placement  Agent has  otherwise  been
     required  to pay by reason  of such  untrue  statement  or  alleged  untrue
     statement or omission or alleged  omission.  No person guilty of fraudulent
     misrepresentation shall be entitled to contribution from any person who was
     not guilty of such fraudulent misrepresentation.

          (e)  The  indemnity  and  contribution  agreements  contained  in this
     Section 7 and the covenants,  warranties and representations of the Company
     contained  in  this  Agreement  shall  remain  in  full  force  and  effect
     regardless of any investigation made by or on behalf of the Placement Agent
     or any  Placement  Agent  Affiliate,  or by or on behalf of the  Company or
     Company  Affiliate,  and shall survive any termination of this Agreement or
     the  issuance  and  delivery of the Shares.  The Company and the  Placement
     Agent  agree  promptly  to  notify  the  other of the  commencement  of any
     litigation  or  proceeding  against  it and,  in the  case of the  Company,
     against any of the  Company  Affiliates,  and in the case of the  Placement
     Agent, any Placement Agent  Affiliate,  in connection with the issuance and
     sale of the  Shares,  or in  connection  with the  Offering  Memorandum  or
     Registration Statement.

     8.  Survival of Certain  Provisions.  The  indemnity  and other  agreements
contained in Section 7 hereof and the  representations  and warranties and other
statements  of the  Company set forth in this  Agreement  or made by the Company
pursuant to this Agreement shall remain in full force and effect,  regardless of
(i) any  termination of this  Agreement,  (ii) any  investigation  made by or on
behalf


                                       14



of the Placement Agent or any of its  controlling  persons or by or on behalf of
the Company or any of its officers,  directors or controlling  persons and (iii)
acceptance of delivery of and payment for Shares.

     9. Effective Time: Termination.

          (a) This Agreement shall become  effective at the earlier of (i) 10:00
     a.m., New York Time, on the first full business day following the execution
     hereof or (ii) the time of the initial offering of any of the Shares by the
     Placement Agent after the execution  hereof.  By giving notice as set forth
     in Section 10 hereof before the time this Agreement becomes effective,  the
     Placement  Agent or the Company may prevent this  Agreement  from  becoming
     effective  without  liability of any party to any other party,  except that
     the Company shall remain  obligated to pay costs and expenses to the extent
     provided in Section 4 of this Agreement.

          (b) The  Placement  Agent  shall  have  the  right to  terminate  this
     Agreement by giving notice as hereinafter specified at any time at or prior
     to the Closing Date, (i) if the Company shall have failed,  refused or been
     unable at or prior to the Closing Date to perform any agreement on its part
     to be performed,  or because any other  condition of the Placement  Agent's
     obligations  hereunder  required  to be  fulfilled  by the  Company  is not
     fulfilled,  or (ii) if trading in securities on the New York Stock Exchange
     shall have been suspended or minimum prices shall have been  established on
     the New York Stock Exchange,  by the New York Stock Exchange or by order of
     the Commission or any other governmental authority having jurisdiction,  or
     (iii) if a banking  moratorium  shall have been  declared by federal or New
     York  authorities,  or (iv) if on or prior to the Closing  Date the Company
     shall have sustained a loss by strike, fire, flood, earthquake, accident or
     other  calamity  of such  character  as to  interfere  materially  with the
     conduct of the business and operations of the Company regardless of whether
     or not such loss shall have been insured, or (v) if there shall have been a
     material adverse change in the general political or economic  conditions or
     financial markets in the United States as in the reasonable judgment of the
     Placement Agent makes it inadvisable or  impracticable  to proceed with the
     offering,  sale and  delivery of the Shares,  or (vi) if on or prior to the
     Closing Date there shall have been any material  outbreak or  escalation of
     hostilities or other national or  international  calamity or crisis of such
     magnitude in its effect on the  financial  markets of the United States as,
     in the reasonable  judgment of the Placement Agent,  makes it impracticable
     or inadvisable to market the Shares.  Any such termination shall be without
     liability  of any party to any other party except as provided in Sections 4
     and 7 hereof.

          If the Placement  Agent elects to prevent this Agreement from becoming
     effective or to terminate  this Agreement as provided in this Section 9, it
     shall promptly  notify the Company by telephone,  telecopy or telegram,  in
     each case  confirmed by letter.  If the Company shall elect to prevent this
     Agreement from becoming  effective,  the Company shall promptly  notify the
     Placement Agent by telephone,  telecopy or telegram, in each case confirmed
     by letter.

          (c) In the event that the Closing shall not have occurred on or before
     August 31, 1998, this Agreement shall terminate at the close of business on
     such date. Any such


                                       15



     termination  shall be  without  liability  of any party to any other  party
     except as provided in Sections 4, 7 and 9(d) hereof.

          (d) In the event of any  termination of this Agreement for any reason,
     if  a  private  placement  of  securities  is  consummated  following  such
     termination on or before November 30, 1998 by the Company with a party that
     the Placement Agent has contacted  regarding the Company pursuant to and as
     part of its  engagement by the Company and that has been  identified to the
     Company in writing prior to or within ten days following such  termination,
     the  Placement  Agent shall be  entitled  to receive a placement  agent fee
     equal to 6% of the gross proceeds  received by the Company for such private
     placement, reimbursement of expenses, and all other amounts provided for in
     this Agreement, as if this Agreement had not been terminated.

     10.  Notice.   Except  as  otherwise   specifically  provided  herein,  all
statements,  requests,  notices and advice hereunder shall be in writing,  or by
telephone  or  telegram if  subsequently  confirmed  in writing,  and, if to the
Placement Agent, shall be sufficient in all respects if delivered or sent to the
Placement Agent at the address set forth in the Offering Memorandum,  and, if to
the  Company,  shall be  sufficient  in all respects if delivered or sent to the
Company  at the  address of its  principal  place of  business  set forth in the
Offering  Memorandum.  Notice shall be deemed given upon the date of delivery or
the date such notice is sent.

     11.  Successors  and  Assigns.  This  Agreement  shall inure  solely to the
benefit of the Company and the  Placement  Agent and, to the extent  provided in
Section  7 hereof,  to any  person or  entity  named in such  Section.  No other
person, partnership,  association or corporation shall acquire or have any right
under or by virtue of this Agreement.  The term  "successors"  shall not include
any  purchaser of any Shares merely  because of such  purchase.  The  respective
rights and  obligations of the Company and the Placement Agent hereunder may not
be assigned, transferred or contracted to another.

     12.  Governing  Law. This  Agreement  shall be governed by and construed in
accordance  with the internal laws of the State of New York,  without  regard to
conflicts of law principles.

     13. Entire  Agreement.  This Agreement is the complete and entire agreement
among  the  parties  with  respect  to the  offer  and  sale of the  Shares  and
supersedes  all prior  written and oral  communications  with  respect  thereto,
specifically  including  any  engagement  letter  with  respect  to the  matters
addressed herein between the Company and the Placement  Agent;  provided however
that the confidentiality agreement contained in the second sentence of Section 3
and in Section 8 of the engagement  letter dated May 4, 1998 between the Company
and the Placement Agent shall remain in full force and effect in accordance with
its  terms.  This  Agreement  may be  amended  only in a writing  signed by both
parties hereto.


                                       16



     14.   Counterparts.   This  Agreement  may  be  executed  in  one  or  more
counterparts,  each of  which  shall be  deemed  an  original,  but all of which
together shall constitute one and the same instrument.


                                       17



     Please  confirm  that the  foregoing  correctly  sets  forth the  agreement
between us by signing in the space provided below for that purpose.

                                                  Very truly yours,

                                                  ENZON, INC.




                                                  By:/s/ ILLEGIBLEs
                                                  ------------------------------
                                                  Its: Presidenrt and CEO
                                                  ------------------------------
AGREED AND ACCEPTED:

SBC WARBURG DILLON READ INC.


By:  /s/ ILLEGIBLE
     --------------------------------------
Its:  Executive Director 
     --------------------------------------


By:  /s/ ILLEGIBLE
     --------------------------------------
Its:  Associate Director
     --------------------------------------