ENZON INC
S-3/A, 1998-07-10
BIOLOGICAL PRODUCTS, (NO DIAGNOSTIC SUBSTANCES)
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           As filed with the Securities and Exchange Commission on July 10, 1998
                                                      Registration No. 333-58269
================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                               AMENDMENT NO. 1 TO
                                    FORM S-3
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933
                            ------------------------

                                   ENZON, INC.
             (Exact name of registrant as specified in its charter)

           DELAWARE                                          22-2372868
(State or other jurisdiction                             (I.R.S. Employer
of incorporation or organization)                        Identification No.)

                20 Kingsbridge Road, Piscataway, New Jersey 08854
                                 (732) 980-4500

(Address,  including zip code,  and telephone  number,  including  area code, of
registrant's principal executive offices)

                                 --------------
                                JOHN CARUSO, ESQ.
                      VICE PRESIDENT, BUSINESS DEVELOPMENT,
                          GENERAL COUNSEL AND SECRETARY
                                   ENZON, INC.
                20 Kingsbridge Road, Piscataway, New Jersey 08854
                                 (732) 980-4500

            (Name, address, including zip code, and telephone number,
                   including area code, of agent for service)
                                 --------------
                                   Copies to:
                             KEVIN T. COLLINS, ESQ.
                              DORSEY & WHITNEY LLP

                    250 Park Avenue, New York, New York 10177
                                 (212) 415-9200

     Approximate date of commencement of proposed sale to the public: As soon as
practicable after this Registration  Statement  becomes  effective.  If the only
securities  being registered on this Form are being offered pursuant to dividend
or interest reinvestment plans, please check the following box. [_]

     If any  securities  being  registered  on this Form are to be  offered on a
delayed or continuous  basis  pursuant to Rule 415 under the  Securities  Act of
1933, other than securities offered only in connection with dividend or interest
reinvestment plans, check the following box. [x]

     If this Form is filed to  register  additional  securities  for an offering
pursuant to Rule 462(b) under the Securities Act, please check the following box
and list  the  Securities  Act  registration  statement  number  of the  earlier
effective registration statement for the same offering. [_]

     If this Form is a  post-effective  amendment  filed pursuant to Rule 462(c)
under the  Securities  Act,  check  the  following  box and list the  securities
registration  statement number of the earlier effective  registration  statement
for the same offering. [_]

     If delivery of the  prospectus is expected to be made pursuant to Rule 434,
please check the following box. [_]

                         CALCULATION OF REGISTRATION FEE

<TABLE>
<CAPTION>
====================================================================================================================================
 Title of Each Class                                    Proposed Maximum     Proposed Maximum                 Amount of
  of Securities to                 Amount to             Offering Price         Aggregate                    Registration
    be Registered                be Registered             per Share          Offering Price                      Fee
- ------------------------------------------------------------------------------------------------------------------------------------
<S>                             <C>                         <C>                <C>                             <C>      
Common Stock $.01 par           3,983,000 shares            $5.53(1)           $22,025,990                     $6,498
value per share
====================================================================================================================================
</TABLE>

(1)  Estimated   solely  for  the  purpose  of  computing   the  amount  of  the
     registration fee in accordance with Rule 457(c) under the Securities Act of
     1933, as amended (the "Securities  Act"),  based on the average of the high
     and low sale  price for the  common  stock,  $.01 par value per share  (the
     "Common Stock") as reported by the Nasdaq Stock Market on June 26, 1998.

     The Registrant  hereby amends this  Registration  Statement on such date or
dates as may be necessary to delay its effective date until the Registrant shall
file a further  amendment  which  specifically  states  that  this  Registration
Statement shall  thereafter  become effective in accordance with Section 8(a) of
the  Securities  Act of 1933 or until the  Registration  Statement  shall become
effective on such date as the Commission,  acting pursuant to said Section 8(a),
may determine.


<PAGE>


     INFORMATION  CONTAINED  HEREIN IS SUBJECT TO  COMPLETION  OR  AMENDMENT.  A
REGISTRATION  STATEMENT  RELATING  TO THESE  SECURITIES  HAS BEEN FILED WITH THE
SECURITIES  AND EXCHANGE  COMMISSION.  THESE  SECURITIES MAY NOT BE SOLD NOR MAY
OFFERS TO BUY BE ACCEPTED PRIOR TO THE TIME THE REGISTRATION  STATEMENT  BECOMES
EFFECTIVE.  THIS  PROSPECTUS  SHALL  NOT  CONSTITUTE  AN  OFFER  TO  SELL OR THE
SOLICITATION OF AN OFFER TO BUY NOR SHALL THERE BE ANY SALE OF THESE  SECURITIES
IN ANY STATE IN WHICH SUCH OFFER,  SOLICITATION  OR SALE WOULD BE UNLAWFUL PRIOR
TO REGISTRATION OR QUALIFICATION UNDER THE SECURITIES LAWS OF ANY SUCH STATE.

                   SUBJECT TO COMPLETION, DATED JULY 10, 1998

                                   PROSPECTUS

                                   ENZON, INC.
                                3,983,000 Shares
                                  Common Stock
                                ($.01 par value)

                            ------------------------

     This prospectus (the  "Prospectus")  relates to the offer and sale of up to
3,983,000  shares (the  "Shares") of common  stock,  $.01 par value (the "Common
Stock"),   of  Enzon,  Inc.  (the  "Company"  or  "Enzon")  by  certain  selling
stockholders  of the  Company  (each a  "Selling  Stockholders").  See  "Selling
Stockholders." The Company will not receive any of the proceeds from the sale of
the Shares.

     The  Selling  Stockholders  may sell the Shares from time to time in one or
more transactions  (which may involve block transactions) in the open market, in
negotiated  transactions,  through the writing of options on the Shares (whether
such options are listed on an options exchange or otherwise) or by a combination
of these methods,  at fixed prices that may be changed,  at market prices at the
time of sale, at prices  related to market prices or at negotiated  prices.  The
Selling  Stockholders may effect these  transactions by selling the Shares to or
through broker-dealers, who may receive compensation in the form of discounts or
commissions  from the Selling  Stockholders or from the purchasers of the Shares
for  whom  the  broker-dealers  may act as  agent  or to whom  they  may sell as
principal,  or both in amounts to be negotiated  immediately  prior to the sale.
The Selling  Stockholders  may also pledge the Shares as  collateral  for margin
accounts or loans and the Shares  could be resold  pursuant to the terms of such
accounts or loans.  The Selling  Stockholders,  such  brokers or dealers and any
other participating brokers or dealers may be deemed to be "underwriters" within
the meaning of the Securities Act of 1933, as amended (the "Securities  Act") in
connection with such sales. See "Plan of Distribution."

     In addition,  any securities  covered by this Prospectus  which qualify for
sale  pursuant  to Rule 144 under the  Securities  Act ("Rule  144") may be sold
under Rule 144 rather than pursuant to this Prospectus.  To the extent required,
the  specific  shares  of  Common  Stock to be sold,  the name of any  successor
Selling  Stockholders,  the public offering price,  the names of any such agent,
dealer or underwriter, and any applicable commission or discount with respect to
any particular offer will be set forth in an accompanying Prospectus Supplement.
See "Selling Stockholders" and "Plan of Distribution."

     Neither the Company nor the Selling Stockholders can presently estimate the
amount of  commissions  or  discounts,  if any, that will be paid by the Selling
Stockholders  on  account of their  sale of the  Shares  from time to time.  The
Company will bear all expenses in connection with the registration of the Shares
herein, which expenses are estimated to be approximately  $184,000.  The Selling
Stockholders  will pay any brokerage  compensation in connection with their sale
of the Shares. See "Use of Proceeds."

     The Company's Common Stock is traded in the over-the-counter  market and is
quoted on The Nasdaq National Market,  under the symbol "ENZN." On July 8, 1998
the last  reported  sale price of the Common  Stock,  as  reported on The Nasdaq
National Market was $6.375 per share.

<PAGE>


         AN INVESTMENT IN THE SECURITIES OFFERED HEREBY INVOLVES A HIGH
            DEGREE OF RISK. SEE "RISK FACTORS" COMMENCING ON PAGE 7.

          THESE SECURITIES HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE
           SECURITIES AND EXCHANGE COMMISSION OR ANY STATE SECURITIES
        COMMISSION, NOR HAS THE SECURITIES AND EXCHANGE COMMISSION OR ANY
        STATE SECURITIES COMMISSION PASSED UPON THE ACCURACY OR ADEQUACY
      OF THIS PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL
                                    OFFENSE.

                  The date of this Prospectus is July __, 1998



<PAGE>




                                TABLE OF CONTENTS

                                                                           Page
                                                                           ----
Available Information ...................................................    2

Incorporation of Certain Documents by Reference .........................    2

Prospectus Summary ......................................................    4

Risk Factors ............................................................    7

Use of Proceeds .........................................................   12

Selling Stockholders ....................................................   12

Plan of Distribution ....................................................   15

Legal Matters ...........................................................   16

Experts .................................................................   16


No  dealer,  salesperson  or  other  person  has  been  authorized  to give  any
not contained or incorporated by reference in this Prospectus in connection with
this offering.  Any information or representation  not contained or incorporated
by  reference  herein  must not be relied on as having  been  authorized  by the
Company,  the Selling  Stockholders or their respective agents.  This Prospectus
does not constitute an offer to sell or the  solicitation of an offer to buy the
securities  offered  hereby in any state to any person to whom it is unlawful to
make  such  offer  or  solicitation.  Except  where  otherwise  indicated,  this
Prospectus speaks as of its date and neither the delivery of this Prospectus nor
any sale made hereunder shall,  under any  circumstances,  create an implication
that  there has been no  change in the  affairs  of the  Company  since the date
hereof  or that the  information  contained  herein  is  correct  as of any time
subsequent to its date.


<PAGE>

                              AVAILABLE INFORMATION

     The Company is subject to the informational  requirements of the Securities
Exchange  Act of 1934,  as  amended  (the  "Exchange  Act"),  and in  accordance
therewith  files  reports,  proxy  statements  and  other  information  with the
Securities  and Exchange  Commission  (the  "Commission").  Such reports,  proxy
statements  and other  information  filed by the  Company can be  inspected  and
copied at the public  reference  facilities  maintained by the Commission at 450
Fifth Street,  N.W.,  Washington,  D.C.  20549,  and at the  following  Regional
Offices of the Commission:  New York Regional Office,  Seven World Trade Center,
Suite 1300, New York, New York 10048; and Chicago Regional Office,  Northwestern
Atrium  Center,  500  West  Madison  Street,   Suite  1400,  Chicago,   Illinois
60661-2511.  Copies of such material can be obtained  from the Public  Reference
Section of the Commission at 450 Fifth Street, N.W.,  Washington,  D.C. 20549 at
prescribed  rates.  The  Commission  also  maintains  a Web site  that  contains
reports, proxy and information regarding the Company at (http://www.sec.gov).

     The  Company's  Common  Stock is listed on the Nasdaq  National  Market and
reports,  proxy and information  statements and other information concerning the
Company can be inspected at the National Association of Securities Dealers, 1735
K Street, N.W., 4th Floor, Washington, D.C. 20006-1506.

     The Company has filed with the Commission a Registration  Statement on Form
S-3 (referred to herein together with all amendments and exhibits thereto as the
"Registration  Statement")  under the Securities Act, with respect to the shares
of Common  Stock  offered  hereby.  This  Prospectus  which  forms a part of the
Registration  Statement,  does not contain all of the  information  set forth or
incorporated  by reference in the  Registration  Statement  and the exhibits and
schedules  thereto,  certain parts of which are omitted in  accordance  with the
rules and regulations of the Commission. For further information with respect to
the Company and the shares of Common Stock offered  hereby,  reference is hereby
made to the Registration  Statement,  including the exhibits thereto.  Copies of
the  Registration  Statement,  including the exhibits,  may be obtained from the
Public Reference  Section of the Commission at the  aforementioned  address upon
payment of the fee  prescribed  by the  Commission.  Copies of each document may
also   be   obtained    through   the    Commission's    internet   address   at
http://www.sec.gov.  The  summaries  contained in this  Prospectus of additional
information  included in the  Registration  Statement or any exhibit thereto are
qualified in their entirety by reference to such information or exhibit.

     The following trademarks and service marks appear in or are incorporated by
reference  into,  this  Prospectus:  ADAGEN(R) and  ONCASPAR(R)  are  registered
trademarks  of the Company;  PEGNOLOGY(R)  is a  registered  service mark of the
Company;  SCA(R) is a registered  trademark  of Enzon Labs Inc., a  wholly-owned
subsidiary  of the Company;  Intron A(R) is a  registered  trademark of Schering
Corporation.

                 INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE

     The Company hereby  incorporates  by reference into this Prospectus (i) its
Annual  Report on Form 10-K for the  Fiscal  Year  Ended  June 30,  1997,  which
contains audited  financial  statements for the Company's latest fiscal year for
which a Form 10-K was required to have been filed and  incorporates by reference
certain  portions of the  Company's  definitive  Proxy  Statement for the Annual
Meeting of  Stockholders  held December 2, 1997, (ii) all other reports filed by
the Company  pursuant to Section  13(a) or 15(d) of the  Exchange Act since June
30, 1997,  including but not limited to, the Quarterly  Reports on Form 10-Q for
the Quarters Ended September 30, 1997,  December 31, 1997 and March 31, 1998 and
the Current Report on Form 8-K filed on June 30, 1998 and (iii) the  description
of the Company's Common Stock,  $.01 par value, as contained in its registration
statement on Form 8-A, filed with the Commission on October 29, 1984, as amended
by a Form 8 filed with the Commission on October 15, 1990.

     All documents filed by the Company  pursuant to Sections  13(a),  13(c), 14
and 15(d) of the Exchange  Act,  subsequent  to the date hereof and prior to the
filing  of a  post-effective  amendment  to  the  Registration  Statement  which
indicates that all shares of Common Stock offered hereby have been sold or which
deregisters all shares of Common Stock then remaining unsold, shall be deemed to
be  incorporated  by reference into this Prospectus and to be a part hereof from
the date of filing of such documents.



                                       2
<PAGE>


     Any statement  contained herein or in a document  incorporated or deemed to
be incorporated by reference herein shall be deemed to be modified or superseded
for purposes of this Prospectus to the extent that such statement is modified or
superseded by a statement  contained herein or in a subsequently  filed document
which also is or is deemed to be  incorporated  by  reference  herein.  Any such
statement so modified or superseded  shall not be deemed,  except as so modified
or superseded, to constitute a part of this Prospectus.

     The Company will provide,  without  charge,  to each person  (including any
beneficial  owner) to whom this  Prospectus is  delivered,  upon written or oral
request of such person,  a copy of any and all of the information  that has been
incorporated  by reference in this  Prospectus  (not including  exhibits to such
information unless such exhibits are specifically incorporated by reference into
such  information).  Such  requests  should be  directed  to John  Caruso,  Vice
President,  Administration,  General  Counsel and  Secretary,  at the  Company's
principal  executive  offices at 20  Kingsbridge  Road,  Piscataway,  New Jersey
08854, telephone (732) 980-4500.


                                       3
<PAGE>


                               PROSPECTUS SUMMARY

The  following  summary  is  qualified  in its  entirety  by the  more  detailed
information  and the  Consolidated  Financial  Statements  and the Notes thereto
appearing elsewhere herein or incorporated by reference in this Prospectus. This
Prospectus and such  documents  contain  various  "forward  looking  statements"
within the meaning of Section 27A of the Securities Act of 1933, as amended (the
"Securities  Act"),  which represent the Company's  intentions,  expectations or
beliefs  concerning  future events,  including,  but not limited to,  statements
regarding  management's  expectations or beliefs concerning future events. These
forward-looking  statements are qualified by important  factors that could cause
actual  results  to  differ   materially  from  those  in  the   forward-looking
statements,  including,  without limitation,  those discussed in "Risk Factors."
See "Risk Factors."

                                   The Company

     Overview

     Enzon  is a  biopharmaceutical  company  that  develops,  manufactures  and
markets  enhanced   therapeutics  for  life-threatening   diseases  through  the
application of its two proprietary technologies: (i) polyethylene glycol ("PEG")
modification and (ii) single-chain  antigen-binding  ("SCA") proteins.  Enzon is
focusing  its  research  activities  primarily  in the area of  oncology  and is
applying its proprietary technologies to compounds of known therapeutic efficacy
in order  to  enhance  the  performance  of  these  compounds.  The  Company  is
commercializing  its proprietary  technologies by developing products internally
and in  cooperation  with  strategic  partners.  To date,  the  Company  and its
partners have  successfully  commercialized  two  products,  ONCASPAR and ADAGEN
(described  below).  The Company  currently has two products  under  development
internally  and has  established  more than 15 strategic  alliances  and license
relationships  for the  development of products using the Company's  proprietary
technologies.  The Company believes that its partners are dedicating substantial
resources to the development of products which incorporate  Enzon's  proprietary
technologies.  These  efforts  include the  development  of  PEG-Intron A, a PEG
modified version of Schering-Plough  Corporation's  ("Schering-Plough") product,
INTRON A  (interferon  alfa 2b), a  genetically-engineered  anticancer-antiviral
drug,  for which  Schering-Plough  is  currently  conducting  Phase III clinical
trials.

     PEG Technology

     The  PEG  process   involves   chemically   attaching   PEG,  a  relatively
non-reactive  and non-toxic  polymer,  to proteins,  chemicals and certain other
pharmaceuticals  for the purpose of enhancing their  therapeutic value (the "PEG
Process").  The  attachment of PEG helps to disguise the compound and reduce the
recognition of the compound by the immune system,  generally  lowering potential
immunogenicity  and  extending  the life of such  compounds  in the  circulatory
system.  The PEG Process also increases the solubility of the modified  compound
which  enhances  the  delivery  of  the  native  compound.   To  date,   Enzon's
commercialized products are PEG modified proteins.  Through enhancements,  Enzon
is seeking to apply its PEG technology to more traditional organic compounds.

     The Company has made significant  improvements to the original PEG Process,
collectively  referred to as Second  Generation PEG Technology,  and has applied
for  and  received  certain  patents  covering  some  improvements.  One  of the
components of the Second  Generation PEG  Technology is new linker  chemistries;
the chemical binding of PEG to unmodified proteins. These new linkers provide an
enhanced  binding of the PEG to the protein  resulting in a more stable compound
with increased  circulation life and may result in more activity of the modified
protein.

     The Company also has developed a Third  Generation PEG  Technology  that is
designed to enable the  technology to be expanded to certain  organic  compounds
and  would  give  such  PEG-modified  compounds  "Pro



                                       4
<PAGE>


Drug"  attributes.  This is accomplished by attaching PEG to a compound by means
of a covalent bond that is designed to break down over time,  thereby  releasing
the active ingredient in the proximity of various tissues.

The Company believes that the "Pro  Drug/Transport  Technology" has much broader
usefulness in that it can be applied to a wide range of small molecules, such as
cancer chemotherapy agents, antibiotics, anti-fungals and immunosuppressants, as
well as to proteins and peptides, including enzymes and growth factors, although
there can be no assurance that such application will result in safe,  effective,
or commercially viable pharmaceutical products.

     Marketed PEG Products

     The Company has received marketing approval from the United States Food and
Drug  Administration  ("FDA") for two first generation PEG technology  products:
(i) ONCASPAR,  the PEG formulation of asparaginase,  for the indication of acute
lymphoblastic  leukemia  ("ALL") in patients  who are  hypersensitive  to native
forms of  L-asparaginase  and (ii)  ADAGEN,  the PEG  formulation  of  adenosine
deaminase, the first successful application of enzyme replacement therapy for an
inherited  disease  to treat a rare  form of  Severe  Combined  Immunodeficiency
Disease ("SCID"), commonly known as the "Bubble Boy Disease."

     ADAGEN is marketed by Enzon on a worldwide  basis.  ONCASPAR is marketed in
the U.S. and Canada by Rhone-Poulenc Rorer Pharmaceuticals,  Inc. and certain of
its  affiliated  entities  ("RPR")  and in Europe by Medac GmbH  ("Medac").  The
Company  has also  granted  exclusive  licenses  to RPR to sell  ONCASPAR in the
Pacific Rim and Mexico.  The  Company is entitled to  royalties  on the sales of
ONCASPAR in North  America by RPR,  as well as  manufacturing  revenue  from the
production of ONCASPAR.  The Company's  agreements  with RPR for the Pacific Rim
and with Medac  require the partners to purchase  ONCASPAR from the Company at a
set price which  increases  over the term of the  agreements.  In addition,  the
agreements  provide for minimum purchase  quantities.  The Company  manufactures
both ADAGEN and ONCASPAR in its South Plainfield, New Jersey facility.

     PEG Products under Development

     The Company currently has three products created using its Second and Third
Generation  PEG  Technology  in clinical and  preclinical  trials.  The first is
PEG-Intron  A, a PEG modified  version of  Schering-Plough's  product,  INTRON A
(interferon alfa 2b), a  genetically-engineered  anticancer-antiviral  drug, for
which  Schering-Plough is currently conducting Phase III clinical trials for use
in the  treatment  of  hepatitis  C. The second  product  under  development  is
PEG-hemoglobin,  a  proprietary  bovine  hemoglobin-based  oxygen-carrier  being
developed  for the  radiosensitization  of solid hypoxic  tumors,  for which the
Company is currently  conducting a Phase Ib clinical  trial.  The third  product
under development is PROTHECAN, a PEG-modified version of camptothecin, a potent
topoisomerase-1  inhibitor,  for use in certain  cancers,  which is currently in
preclinical studies.

     PEG-Intron A. PEG-Intron A was developed by the Company in conjunction with
Schering-Plough  to have longer lasting  activity and an enhanced safety profile
compared to the currently  marketed form of INTRON A.  PEG-Intron A is currently
in a large scale Phase III clinical  trial in hepatitis C patients in the United
States and Europe.  Other indications being pursued include chronic  myelogenous
leukemia and solid tumors. It is expected that PEG-Intron A will be administered
once a week,  compared to the current  regimen for unmodified  INTRON A of three
times a week. Moreover,  it is anticipated that PEG-Intron A will provide a more
convenient  dosing schedule with an improved side effect profile and an improved
therapeutic index for hepatitis C patients. Currently, some patients on INTRON A
experience debilitating flu-like symptoms.

     Pursuant to an  agreement  with  Schering-Plough,  the Company will receive
royalties on worldwide sales of PEG-Intron A, receive  milestone  payments,  and
has the option to be the  exclusive  manufacturer  of  PEG-Intron A for the U.S.
market.  Schering-Plough's  sales of INTRON A were approximately $598 million in
1997


                                       5
<PAGE>


for all approved indications. The worldwide market for alpha interferon products
is  estimated to be in excess of $1 billion for all  approved  indications.  The
patents  covering  Schering-Plough's  INTRON A will begin to expire in 2001. The
Company's  Second  Generation  PEG  Technology  patents  that cover the modified
product should afford Schering-Plough extended patent life for PEG Intron-A.

SCA Technology

     The  Company  also  has an  extensive  licensing  program  for  its  second
proprietary  technology,  SCA protein  technology.  SCA proteins are genetically
engineered  proteins designed to overcome the problems  hampering the diagnostic
and therapeutic use of conventional  monoclonal antibodies.  Preclinical studies
have shown that certain SCA proteins  target and  penetrate  tumors more readily
than  conventional  monoclonal  antibodies.  In  addition  to these  advantages,
because SCA proteins are developed at the gene level, they are better suited for
targeted  delivery of gene therapy  vectors and  fully-human SCA proteins can be
isolated directly, with no need for costly "humanization" procedures. Also, many
gene therapy  methods require that proteins be produced in an active form inside
cells. SCA proteins can be produced  through  intracellular  expression  (inside
cells) more readily than monoclonal antibodies.

     Currently,  there are nine SCA proteins in Phase I or II clinical trials by
various   corporations  and   institutions.   Two  of  these   corporations  and
institutions  have  existing  licenses  with the  Company  with  respect  to SCA
proteins and others are expected to require similar licenses.  Some of the areas
being  explored are cancer  therapy,  cardiovascular  indications  and AIDS. The
Company has granted  non-exclusive  SCA licenses to more than a dozen companies,
including Bristol-Myers Squibb Company, Baxter Healthcare Corporation, Eli Lilly
& Co.,  Alexion  Pharmaceuticals  Inc.,  and the Gencell  division of RPR. These
licenses  generally  provide  for  upfront  payments,   milestone  payments  and
royalties on sales of FDA approved products.

     The  Company's  principal  executive  office  and  mailing  address  is  20
Kingsbridge  Road,  Piscataway,  New Jersey 08054,  and its telephone  number is
(732) 980-4500.

                                                   The Offering

Securities Offered............     This Prospectus relates to an offering by the
                                   Selling   Stockholders  of  up  to  3,983,000
                                   shares of Common Stock of the Company.

Securities Outstanding(1)          As of May 29, 1998 the Company had 31,331,081
                                   shares of  Common  Stock  outstanding.  After
                                   giving  effect  to  the   completion  of  the
                                   private   offering   described   in  "Selling
                                   Stockholders,"   the   Company   would   have
                                   35,314,081    shares    of    Common    Stock
                                   outstanding.

Use of Proceeds ..............     The Company  will not  receive  any  proceeds
                                   from the sale of the Shares offered herein by
                                   the   Selling   Stockholders.   See  "Use  of
                                   Proceeds."

Risk Factors .................     See  "Risk   Factors"  for  a  discussion  of
                                   certain   risk   factors   that   should   be
                                   considered   by   prospective   investors  in
                                   connection  with an  investment in the shares
                                   of Common Stock offered hereby.
- ----------
(1) Excludes 5,417,422 shares reserved for issuance upon exercise of options and
warrants  outstanding at May 29, 1998, at weighted  average  exercise  prices of
$4.03 and $4.17, respectively.


                                       6
<PAGE>


                                  RISK FACTORS

     Information  contained  and  incorporated  by reference in this  Prospectus
contains  "forward-looking  statements"  which can be  identified  by the use of
forward-looking  terminology  such  as  "believes,"  "expects,"  "may,"  "will,"
"should," or "anticipates"  or the negative thereof or other variations  thereon
or comparable  terminology,  or by discussions of strategy.  No assurance can be
given that the future results covered by the forward-looking  statements will be
achieved.  The risk  factors set forth below  constitute  cautionary  statements
identifying  important factors with respect to such forward-looking  statements,
including  certain risks and  uncertainties,  that could cause actual results to
vary  materially  from the  future  results  indicated  in such  forward-looking
statements.  Other  factors could also cause actual  results to vary  materially
from the future results indicated in such forward-looking statements.

     An investment in the Shares offered hereby  involves a high degree of risk.
Prospective  investors should  carefully  consider the following risk factors in
addition to the other  information  set forth and  incorporated  by reference in
this Prospectus before making any decision to invest in the Shares.

Accumulated  Deficit and  Uncertainty of Future  Profitability.  The Company was
originally  incorporated  in 1981. To date,  the Company's  sources of cash have
been the  proceeds  from the sale of its  stock  through  public  offerings  and
private  placements,   sales  of  its  FDA  approved  products,   ADAGEN(R)  and
ONCASPAR(R);  sales of its products for research purposes; contract research and
development fees; technology transfer and license fees; and royalty advances. At
March 31, 1998, the Company had an accumulated  deficit of approximately  $114.5
million.  The  Company  expects to incur  operating  losses for the  foreseeable
future.  To date, ADAGEN and ONCASPAR are the only products of the Company which
have been approved for  marketing in the United  States by the FDA,  having been
approved in March 1990 and February 1994,  respectively.  In addition,  ONCASPAR
has been  approved  for  marketing  in Canada,  Germany and Russia.  In order to
achieve profitable  operations on a continuing basis, the Company,  either alone
or through its  partners,  must  successfully  manufacture,  market and sell its
ADAGEN and ONCASPAR  products and develop,  manufacture and market the Company's
products  which are under  development.  These products are in various stages of
development,  and the period necessary to achieve regulatory approval and market
acceptance of any  individual  product is uncertain and  typically  lengthy,  if
achievable at all.  Potential  investors  should be aware of the  difficulties a
biopharmaceutical enterprise such as the Company encounters,  especially in view
of the intense  competition in the pharmaceutical  industry in which the Company
competes.  There  can be no  assurance  that the  Company's  plans  will  either
materialize or prove  successful,  that its products under  development  will be
successfully developed or that its products will generate revenues sufficient to
enable the Company to achieve profitability.

     Raw Materials and Dependence Upon Suppliers. Except for PEG-hemoglobin, the
Company purchases the unmodified compounds utilized in its approved products and
products under  development  from outside  suppliers.  There can be no assurance
that the purified bovine  hemoglobin  used in the manufacture of  PEG-hemoglobin
can be produced by the  Company in the amounts  necessary  to expand the current
clinical trials. The Company may be required to enter into supply contracts with
outside suppliers for certain unmodified compounds. The Company does not produce
the  unmodified  adenosine  deaminase  used in the  manufacture  of ADAGEN,  the
unmodified forms of  L-asparaginase  used in the manufacture of ONCASPAR and the
unmodified  camptothecin used in the Company's  PROTHECAN product which is under
development and has a supply contract with an outside supplier for the supply of
each of these  unmodified  compounds.  Delays in  obtaining  or an  inability to
obtain  any  unmodified  compound,  including  unmodified  adenosine  deaminase,
unmodified  L-asparaginase,  unmodified bovine blood, or unmodified camptothecin
on reasonable  terms,  or at all,  could have a material  adverse  effect on the
Company's business,  financial condition and results of operations. In the event
the Company is required to obtain an alternate source for an unmodified compound
utilized in a product which is being sold  commercially  or which is in clinical
development, the FDA and relevant foreign regulatory agencies 


                                        7
<PAGE>


will likely require the Company to perform additional testing, which would cause
delays and additional  expenses,  to demonstrate that the alternate  material is
biologically  and chemically  equivalent to the unmodified  compound  previously
used. Such evaluations could include chemical, pre-clinical and clinical studies
and could delay  development  of a product  which is in clinical  trials,  limit
commercial  sales  of an  approved  product  and  cause  the  Company  to  incur
significant  additional expenses. If such alternate material is not demonstrated
to be chemically and  biologically  equivalent to the previously used unmodified
compound,  the  Company  will  likely be  required  to repeat some or all of the
pre-clinical and clinical trials  conducted for such compound.  The marketing of
an FDA approved drug could be disrupted while such tests are conducted.  Even if
the alternate material is shown to be chemically and biologically  equivalent to
the previously used compound,  the FDA or relevant foreign regulatory agency may
require the Company to conduct  additional  clinical  trials with such alternate
material.

Patents and Proprietary Technology. The Company has licensed, and been issued, a
number of patents in the United States and other  countries and has other patent
applications pending to protect its proprietary technology. Although the Company
believes that its patents provide certain protection from competition, there can
be no  assurance  that  such  patents  will  be  of  substantial  protection  or
commercial benefit to the Company,  will afford the Company adequate  protection
from competing  products,  will not be challenged or declared  invalid,  or that
additional United States patents or foreign patent equivalents will be issued to
the  Company.  The scope of patent  claims for  biotechnological  inventions  is
uncertain and the Company's patents and patent  applications are subject to this
uncertainty.  The  Company  is  aware  of  certain  issued  patents  and  patent
applications  belonging  to third  parties,  and there may be other  patents and
patent  applications,  containing  subject  matter  which  the  Company  or  its
licensees  or  collaborators  may  require  in order  to  research,  develop  or
commercialize at least some of the Company's products. There can be no assurance
that licenses  under such patents and patent  applications  will be available on
acceptable terms or at all. If the Company does not obtain such licenses,  it or
its partners could  encounter  delays in product market  introductions  while it
attempts  to design  around  such  patents or could  find that the  development,
manufacture or sale of products requiring such licenses could be foreclosed.  If
the Company does obtain such  licenses it will in all  likelihood be required to
make  royalty and other  payments to the  licensors,  thus  reducing the profits
realized by the Company from the products covered by such licenses.  The Company
is aware that certain  organizations  are engaging in  activities  that infringe
certain  of the  Company's  PEG  technology  and SCA  patents.  There  can be no
assurance  that the Company  will be able to enforce its patent and other rights
against such  organizations.  The Company  expects that there may be significant
litigation in the industry  regarding patents and other proprietary  rights and,
if  Enzon  were to  become  involved  in such  litigation,  it could  consume  a
substantial amount of the Company's resources.  In addition,  the Company relies
heavily on its proprietary  technologies  for which pending patent  applications
have been filed and on unpatented know-how developed by the Company.  Insofar as
the Company  relies on trade  secrets and  unpatented  know-how to maintain  its
competitive  technological  position,  there can be no assurance that others may
not independently develop the same or similar technologies. Although the Company
has  taken  steps  to  protect  its  trade  secrets  and  unpatented   know-how,
third-parties  nonetheless may gain access to such information.  The Company has
two research and license  agreements  with The Green Cross  Corporation  ("Green
Cross")  regarding  rHSA. The Company and Yoshitomi  Pharmaceutical  Industries,
Ltd.  ("Yoshitomi"),  the successor to Green Cross'  business,  are currently in
arbitration to resolve the amount of royalties that will be due the Company,  if
any. In April 1998,  Yoshitomi  filed  documents in such  arbitration  seeking a
declaratory  judgment that under its agreement with the Company no royalties are
payable.  Any adverse decision from such an arbitration  proceeding could result
in a  material  adverse  effect  to the  Company's  future  business,  financial
condition and results of operations.  Research  Corporation  Technologies,  Inc.
("Research  Corporation") held the original patent upon which the PEG Process is
based and had  granted  the  Company  a  license  under  such  patent.  Research
Corporation's  patent  for  the  PEG  Process  in  the  United  States  and  its
corresponding  foreign  patents have expired.  Although the Company has obtained
several improvement patents in connection with the PEG Process,  there can be no
assurance  that  any of  these  patents  will  enable  the  Company  to  prevent
infringement or that competitors will not develop  competitive  products outside
the protection  that may be afforded by these patents.  The Company is aware 



                                       8
<PAGE>


that others have also filed patent applications and have been granted patents in
the United States and other  countries with respect to the application of PEG to
proteins  and  other  compounds.  Based  upon  the  expiration  of the  Research
Corporation  patent,  other  parties  will be  permitted  to make,  use, or sell
products covered by the claims of the Research  Corporation  patent,  subject to
other patents,  including  those held by the Company.  There can be no assurance
that the expiration of the Research  Corporation patent will not have a material
adverse effect on the business, financial condition and results of operations of
the Company.

Limited Sales and Marketing Experience;  Dependence on Marketing Partners. Other
than ADAGEN,  which the Company  markets on a worldwide basis to a small patient
population,  the Company does not engage in the direct  commercial  marketing of
any of its products and therefore does not have significant  sales and marketing
experience.  For certain of its  products,  the Company has  provided  exclusive
marketing  rights to its  corporate  partners  in  return  for  royalties  to be
received on sales.  With respect to ONCASPAR,  the Company has granted exclusive
marketing  rights in North  America and the Pacific Rim to RPR.  The Company has
also granted  exclusive  marketing rights in Europe and Russia to Medac Gmbh and
in Israel  to Tzamal  Pharma  Ltd..  The  Company  expects  to retain  marketing
partners to market ONCASPAR in other foreign markets, principally South America,
and is currently pursuing arrangements in this regard. There can be no assurance
that such  efforts  will result in the  Company  concluding  such  arrangements.
Regarding the marketing of certain of the Company's other future  products,  the
Company  expects to evaluate  whether to create a sales force to market  certain
products in the United States or to continue to enter into license and marketing
agreements with others for United States and foreign  markets.  These agreements
generally  provide that all or a  significant  portion of the marketing of these
products will be conducted by the Company's licensees or marketing partners.  In
addition,  under  certain  of  these  agreements,  the  Company's  licensees  or
marketing partners may have all or a significant  portion of the development and
regulatory approval responsibilities. There can be no assurance that the Company
will be able to control the amount and timing of resources  that any licensee or
marketing  partner may devote to the Company's  products or prevent any licensee
or marketing  partner from pursuing  alternative  technologies  or products that
could result in the  development  of products  that  compete with the  Company's
products and the  withdrawal of support for the Company's  products.  Should the
licensee  or  marketing  partner  fail to develop a  marketable  product (to the
extent it is responsible  for product  development)  or fail to market a product
successfully,  if it is developed,  the Company's business,  financial condition
and results of operations may be adversely  affected.  There can be no assurance
that the Company's  marketing  strategy will be successful.  Under the Company's
marketing and license agreements, the Company's marketing partners and licensees
may have the right to  terminate  the  agreements  and  abandon  the  applicable
products at any time for any reason without significant payments. The Company is
aware that certain of its marketing  partners are pursuing parallel  development
of products on their own and with other collaborative partners which may compete
with the  licensed  products and there can be no  assurance  that the  Company's
other  current or future  marketing  partners will not also pursue such parallel
courses.

Reimbursement from Third-Party  Payors.  Sales of the Company's products will be
dependent in part on the availability of reimbursement from third-party  payors,
such as governmental health administration authorities,  private health insurers
and  other   organizations.   Government  and  other   third-party   payors  are
increasingly  sensitive to the containment of health care costs and are limiting
both coverage and levels of reimbursement for new therapeutic  products approved
for  marketing,  and are  refusing,  in some cases,  to provide any coverage for
indications for which the FDA and other national health  regulatory  authorities
have not  granted  marketing  approval.  There  can be no  assurance  that  such
third-party payor  reimbursement will be available or will permit the Company to
sell its products at price levels  sufficient  for it to realize an  appropriate
return on its  investment  in product  development.  Since  patients who receive
ADAGEN  will be  required  to do so for  their  entire  lives  (unless a cure or
another treatment is developed),  lifetime limits on benefits which are included
in most  private  health  insurance  policies  could  permit  insurers  to cease
reimbursement for ADAGEN. Lack of or inadequate  reimbursement by government and
other  third  party  payors  for the  Company's  products  would have a material
adverse  effect on the Company's  business,  financial  condition and results of
operations.


                                       9
<PAGE>


Government  Regulation.   The  manufacturing  and  marketing  of  pharmaceutical
products in the United  States and abroad is subject to  stringent  governmental
regulation  and the sale of any of the  Company's  products for use in humans in
the United States will require the prior approval of the FDA. Similar  approvals
by  comparable  agencies  are required in most  foreign  countries.  The FDA has
established  mandatory  procedures  and  safety  standards  which  apply  to the
clinical  testing,   manufacture  and  marketing  of  pharmaceutical   products.
Pharmaceutical  manufacturing  facilities are also regulated by state, local and
other authorities. Obtaining FDA approval for a new therapeutic may take several
years and involve  substantial  expenditures.  ADAGEN was approved by the FDA in
March 1990.  ONCASPAR  was approved by the FDA in February  1994,  in Germany in
November  1994 and in  Canada  in 1997 in each  case  for  patients  with  acute
lymphoblastic leukemia who are hypersensitive to native forms of L-asparaginase.
ONCASPAR was approved in Russia for therapeutic use in a broad range of cancers.
Except for these  approvals,  none of the  Company's  other  products  have been
approved for sale and use in humans in the United States or elsewhere. There can
be no assurance  that the Company will be able to obtain FDA approval for any of
its other products. In addition, any approved products are subject to continuing
regulation,  and  noncompliance by the Company with applicable  requirements can
result in  criminal  penalties,  civil  penalties,  fines,  recall  or  seizure,
injunctions  requiring  suspension  of  production,   orders  requiring  ongoing
supervision  by the FDA or refusal by the  government  to approve  marketing  or
export  applications  or to allow the  Company to enter into  supply  contracts.
Failure to obtain or maintain  requisite  governmental  approvals  or failure to
obtain or maintain approvals of the scope requested,  will delay or preclude the
Company or its licensees or marketing partners from marketing their products, or
limit the  commercial  use of the  products,  and  thereby  may have a  material
adverse  affect on the Company's  business,  financial  condition and results of
operations.

Intense  Competition and Risk of  Technological  Obsolescence.  Many established
biotechnology and pharmaceutical  companies with resources greater than those of
the Company are engaged in activities  that are  competitive  with the Company's
and may  develop  products  or  technologies  which  compete  with  those of the
Company.  The Company is aware that other companies are engaged in utilizing PEG
technology  in  developing  drug  products.  There can be no assurance  that the
Company's  competitors  will not  successfully  develop,  manufacture and market
competing  products  utilizing  PEG  technology  or  otherwise.  Other  drugs or
treatment  modalities which are currently  available or that may be developed in
the  future,  and which treat the same  diseases  as those  which the  Company's
products are designed to treat, may be competitive with the Company's  products.
There can be no assurance that the Company will be able to compete  successfully
against current or future  competitors or that such  competition will not have a
material  adverse  effect on the  Company's  business,  financial  condition and
results of operations.  Rapid technological  development by others may result in
the  Company's   products  becoming  obsolete  before  the  Company  recovers  a
significant portion of the research,  development and commercialization expenses
incurred with respect to those products.  The Company's success,  in large part,
depends  upon  developing  and   maintaining  a  competitive   position  in  the
development of products and  technologies in its area of focus.  There can be no
assurance  that  the  Company's  competitors  will  not  succeed  in  developing
technologies  or products that are more  effective than any which are being sold
or developed by the Company or which would render the Company's  technologies or
products  obsolete  or  noncompetitive.  The  Company's  failure to develop  and
maintain a competitive position with respect to its products and/or technologies
would have a material  adverse effect on its business,  financial  condition and
results of operations.

Uncertainty of Market Acceptance.  The Company's products,  ONCASPAR and ADAGEN,
have  been  approved  by the FDA to  treat  patients  with  acute  lymphoblastic
leukemia  and  a  rare  form  of  severe  combined   immunodeficiency   disease,
respectively.  Neither  product has become  widely used due to the small patient
population and limited  indications  approved by the FDA. The Company's  current
research  and   development   efforts  are  directed   towards   developing  new
technologies  to aid in drug  delivery.  Assuming  that the  Company  is able to
develop such  technologies  and secure the requisite FDA  approvals,  the market
acceptance of any such  products will depend upon the  acceptance by the medical
community of the use of such  technologies.  There can be no assurance  that any
additional  products  will be  approved  by the FDA or that,  if  approved,  the
medical


                                       10
<PAGE>


community  will use them.  In addition,  the use of any such new  products  will
depend upon the extent of third party medical reimbursement, increased awareness
of the  effectiveness  of such  technologies and sales efforts by the Company or
any marketing  partner.  The Company's  proprietary  PEG technology has received
only limited  market  acceptance to date.  Failure of the Company to develop new
FDA approved  products and to achieve market  acceptance for such products would
have a material adverse effect on the Company's  business,  financial  condition
and results of operation.

Potential Product Liability. The use of the Company's products during testing or
after  regulatory  approval  entails an inherent  risk of adverse  effects which
could  expose the Company to product  liability  claims.  The Company  maintains
product  liability  insurance  coverage  in the total  amount of $10 million for
claims  arising  from the use of its  products in clinical  trials  prior to FDA
approval and for claims arising from the use of its products after FDA approval.
There can be no assurance that the Company will be able to maintain its existing
insurance  coverage or obtain  coverage for the use of its other products in the
future. There can be no assurance that such insurance coverage and the resources
of the Company  would be  sufficient  to satisfy any  liability  resulting  from
product  liability  claims or that a product  liability  claim  would not have a
material  adverse  effect on the  Company's  business,  financial  condition  or
results of operations.

Future Capital Needs; Uncertainty of Additional Financing. The Company's current
sources of liquidity  are its cash  reserves,  and interest  earned on such cash
reserves,  sales of ADAGEN and  ONCASPAR,  sales of its  products  for  research
purposes,  and license fees.  There can be no assurance as to the level of sales
of the Company's FDA approved  products,  ADAGEN and ONCASPAR,  or the amount of
royalties  realized  from  the  commercial  sale  of  ONCASPAR  pursuant  to the
Company's  licensing  agreements.  Total  cash  reserves,  including  short term
investments,  as of March 31, 1998, were approximately  $6.6 million,  and after
giving effect to the  approximately  $17,600,000 of net proceeds received by the
Company  from the  private  placement  of the  Shares  offered  herein,  will be
approximately  24,228,000.   Based  upon  its  currently  planned  research  and
development  activities and related costs and its current  sources of liquidity,
the Company anticipates its current cash reserves will be sufficient to meet its
capital and operational  requirements for the foreseeable  future. The Company's
future  needs and the  adequacy  of  available  funds  will  depend on  numerous
factors, including without limitation,  the successful  commercialization of its
products,  progress in its product development  efforts, the magnitude and scope
of such efforts, progress with preclinical studies and clinical trials, progress
with regulatory affairs activities, the cost of filing,  prosecuting,  defending
and enforcing patent claims and other  intellectual  property rights,  competing
technological  and  market  developments,   and  the  development  of  strategic
alliances for the marketing of its products.  There can be no assurance that the
Company will not require additional  financing for its currently planned capital
and  operational  requirements.  In  addition,  the  Company may seek to acquire
additional  technology,  enter into strategic alliances and engage in additional
research and development programs,  which may require additional financing.  The
Company does not have any committed sources of additional  financing,  and there
can be no assurance that additional funding, if necessary,  will be available on
acceptable  terms,  if at all.  To the  extent  the  Company is unable to obtain
financing,  it may be  required  to curtail its  activities  or sell  additional
securities.  There can be no assurance  that any of the  foregoing  fund raising
activities  will  successfully  meet the Company's  anticipated  cash needs.  If
adequate funds are not available,  the Company's  business,  financial condition
and results of operations will be materially and adversely affected.

Dividend  Policy and  Restrictions.  The  Company has paid no  dividends  on its
Common  Stock,  since its  inception  and does not plan to pay  dividends on its
Common  Stock in the  foreseeable  future.  Except as may be utilized to pay the
dividends  payable on the Company's  Series A Cumulative  Convertible  Preferred
Stock (the  "Series A  Preferred  Stock"),  any  earnings  which the Company may
realize will be retained to finance the growth of the Company. In addition,  the
terms of the Series A Preferred Stock restrict the payment of dividends on other
classes and series of stock.


                                       11
<PAGE>


Possible  Volatility  of Stock  Price.  Historically,  the  market  price of the
Company's  Common Stock has  fluctuated  over a wide range and it is likely that
the price of the  Common  Stock  will  fluctuate  in the  future.  Announcements
regarding technical innovations,  the development of new products, the status of
corporate collaborations and supply arrangements,  regulatory approvals,  patent
or proprietary  rights or other  developments  by the Company or its competitors
could have a  significant  impact on the market  price of the Common  Stock.  In
addition,  due to one or more of the  foregoing  factors,  in one or more future
quarters, the Company's results of operations may fall below the expectations of
securities  analysts  and  investors.  In that  event,  the market  price of the
Company's Common Stock could be materially and adversely affected.

Shares  Eligible  for  Future  Sale.  As  of  May  29,  1998,  the  Company  had
approximately  31,331,000  shares of Common Stock  outstanding  and after giving
effect to the consummation of the private offering of 3,983,000 shares of Common
Stock described in "Selling Stockholders" which are offered hereby, but assuming
no additional  shares are issued  pursuant to outstanding  options,  warrants or
convertible securities, would have had approximately 35,314,081 shares of Common
Stock  outstanding.  The  3,983,000  shares of Common Stock  offered  hereby are
"restricted  securities,"  as  that  term  is  defined  in Rule  144  under  the
Securities Act, which when sold pursuant to the  Registration  Statement will be
freely  transferrable  without  restrictions  under the Securities Act, assuming
such Shares are held by  non-affiliates  of the Company.  Of the other shares of
Common Stock  outstanding,  approximately  31,274,000 shares will be immediately
available for sale without  restriction  in the public market and  approximately
26,000 shares will be eligible for sale under Rule 144 of the Securities Act. In
addition,  the  approximately  245,000  shares of  Common  Stock  issuable  upon
conversion  of the Series A Preferred  Stock will be  immediately  available for
sale without  restriction in the public market when issued.  Certain  holders of
the Company's  securities are entitled to registration rights with respect to an
aggregate  of  approximately   1,886,000  shares  of  Common  Stock,   including
approximately  1,039,000 shares underlying outstanding warrants. Of such shares,
approximately  989,000 shares are registered  currently on Form S-3 registration
statements.  The  approximately  4,378,000  shares  of Common  Stock  underlying
outstanding  options which are held by employees,  directors and consultants are
registered on Form S-8 registration statements.  Sales of substantial amounts of
such shares in the public  market or the prospect of such sales could  adversely
affect the market price of the Common Stock.

Anti-takeover  Considerations.  The  Company  has the  authority  to issue up to
3,000,000  shares of Preferred Stock of the Company in one or more series and to
fix the powers,  designations,  preferences  and relative rights thereof without
any further vote of  shareholders.  The issuance of such  Preferred  Stock could
dilute the voting powers of holders of Common Stock and could have the effect of
delaying,  deferring or  preventing a change in control of the Company.  Certain
provisions of the Company's  Articles of  Incorporation  and By-laws,  including
those providing for a staggered Board of Directors, as well as Delaware law, may
operate in a manner that could discourage or render more difficult a takeover of
the  Company  or the  removal  of  management  or may limit  the  price  certain
investors may be willing to pay for shares of Common Stock.

                                 USE OF PROCEEDS

     The  Company  will not  receive  any  proceeds  from the sale of the Shares
offered herein by the Selling Stockholders.  Expenses expected to be incurred by
the Company in connection with this offering are estimated to be $184,000.

                              SELLING STOCKHOLDERS

     The Shares covered by this  Prospectus  were acquired from the Company in a
private  offering  pursuant to Common Stock Purchase  Agreements  (the "Purchase
Agreements") for an aggregate  purchase price of $18,919,250  ($4.75 per share).
The  offer  and  sale  by  the  Company  of the  Common  Stock  to  the  Selling
Stockholders  pursuant  to the  Purchase  Agreements  was  made  pursuant  to an
exemption from the registration



                                       12
<PAGE>


requirements  of the  Securities  Act  provided  by Section  4(2)  thereof.  The
Purchase  Agreements contain  representations  and warranties as to each Selling
Stockholder's status as an "accredited investor" as such term is defined in Rule
501  promulgated  under the  Securities  Act.  Warburg Dillon Read LLC (formerly
known as SBC Warburg Dillon Read Inc.) ("Dillon Read"), the placement agent, was
paid a fee of $900,000 or approximately 4.75% of the aggregate purchase price in
connection  with  the  sale  of  the  Shares  by  the  Company  to  the  Selling
Stockholders  pursuant to the  Purchase  Agreements.  In  addition,  the Company
agreed to reimburse  Dillon Read for its travel,  legal and other  out-of-pocket
expenses  incurred in  connection  with the sale of the Shares by the Company to
the Selling Stockholders  pursuant to the Purchase Agreements up to a maximum of
$50,000. The Company paid Evolution Capital, a broker/dealer,  a fee of $235,155
or  approximately  1.25% of the aggregate  purchase price in connection with the
sale of the Shares by the  Company to the Selling  Stockholders  pursuant to the
Purchase Agreements.

     Pursuant  to  the  Purchase   Agreements,   each  Selling  Stockholder  has
represented  that he,  she or it  acquired  the  Shares  for its own  account as
principal, for investment purposes only, and not with a present view to, or for,
the resale distribution  thereof, in whole or in part, within the meaning of the
Securities Act or any state securities law. The Company agreed, in such Purchase
Agreements, to use its best efforts to prepare and file a registration statement
for the resale of the Shares no later than 10 days after the  effective  date of
the  Purchase  Agreements  and to bear  all  expenses  in  connection  with  the
offering,  other than selling commissions,  underwriting fees and stock transfer
taxes applicable to the Shares and all fees and disbursements of counsel for any
Selling Stockholder. Accordingly, in order to permit the Selling Stockholders to
sell the Shares  when each deems  appropriate,  the  Company  has filed with the
Commission a Registration  Statement on Form S-3, of which this Prospectus forms
a part,  with respect to the resale of the Shares from time to time as described
herein and has agreed to prepare and file such amendments and supplements to the
Registration  Statement as may be necessary to keep the  Registration  Statement
effective  until all Shares  offered  hereby have been sold pursuant  thereto or
until  such  shares  are no  longer,  by reason of Rule 144 or any other rule of
similar  effect,  required to be registered  for the sale thereof by the Selling
Stockholders.

     Except  as  otherwise  described  in  "Stock  Ownership,"  prior  to  their
acquisition  of the  Shares,  none of the  Selling  Stockholders  had a material
relationship with the Company.

     In connection  with the  registration of the shares of Common Stock offered
hereby, the Company will supply prospectuses to the Selling Stockholders.

Stock Ownership

     The table  below sets forth (i) the number of shares of Common  Stock owned
beneficially by the Selling  Stockholders as of July 1, 1998; (ii) the number of
shares of Common  Stock being  offered by the Selling  Stockholders  pursuant to
this  Prospectus;  (iii)  the  number  of  shares  of  Common  Stock to be owned
beneficially  by the Selling  Stockholders  after  completion  of the  offering,
assuming that all of the Shares offered hereby are sold; and (iv) the percentage
of the  outstanding  shares  of  Common  Stock to be owned  beneficially  by the
Selling Stockholders after completion of the offering,  assuming that all of the
Shares offered hereby are sold.


                                       13
<PAGE>


<TABLE>
<CAPTION>
                                                                             Number of           Percentage of
                                                                           Shares to be       Outstanding Shares
                                      Number of                                Owned            of Common Stock
                                       Shares                              Beneficially           to be Owned
                                    Beneficially         Number of             After          Beneficially After
                                     Owned as of           Shares           Completion            Completion
Selling Stockholders                July 1, 1998          Offered          of Offering(1)         of Offering(1)
- --------------------                ------------          --------         --------------     ------------------

<S>                                  <C>                  <C>                 <C>                       <C>
DCF Life Sciences Fund Ltd.          200,000              200,000                   0                     0  
                                                                                                             
DCF Partners, L.P.                   853,000              853,000                   0                     0  
                                                                                                             
Oracle Partners, L.P.                589,589              315,789             273,800                     *  
                                                                                                             
Oracle Institutional Partners,                                                                               
L.P.                                 135,996               78,496              57,500                     *
                                                                                                             
GSAM Oracle Fund, Inc.               306,721              168,721             138,000                     *  
                                                                                                             
Hausmann Holdings, N.V.               88,226               50,526              37,700                     *  
                                                                                                             
Oracle Offshore Ltd.                  36,046               18,046              18,000                     *  
                                                                                                             
Warburg Dillon Read, LLC(2)          517,900              500,000              17,900                     *  
                                                                                                             
Caduceus Capital, L.P.               105,000              105,000                   0                     0  
                                                                                                             
Caduceus Capital Ltd.                220,000              220,000                   0                     0  
                                                                                                             
Marlin BioMed L.P.                    21,053               21,053                   0                     0  
                                                                                                             
Deutsche Vermogen                                                                                            
Sbildungsgesell Shaft mbH            294,737              294,737                   0                     0  
                                                                                                             
                                                                                                            
The Aries Trust                    1,340,868              747,368             593,500                   1.9  
                                                                                                             
Aries Domestic Fund, L.P.            547,964              305,264             242,700                     *  
                                                                                                             
Wayne P. Rothbaum(3)                  58,000               30,000              28,000                     *  
                                                                               
Mitchell D. Silber(3)                 35,000               15,000              20,000                     *  
                                                                                                             
New Technologies Fund                 90,000               60,000              30,000                     *  
</TABLE>                                                               

*  Less than 1%.

(Notes continued on following page)

                                       14
<PAGE>


(1)  Based upon  31,332,831  shares of Common  Stock  outstanding  as of July 1,
     1998.  Assumes  all  Shares  registered  hereby  are sold and that no other
     shares of Common Stock owned by the Selling Stockholders as of July 1, 1998
     are sold.  Since the  Selling  Stockholders  may sell all,  some or none of
     their Shares,  no actual  determination can be made of the aggregate number
     of shares that each Selling  Stockholder  will own upon  completion  of the
     offering to which this Prospectus relates.

(2)  Warburg  Dillon Read LLC (formerly  known as SBC Warburg  Dillon Read Inc.)
     acted as the placement  agent in the private  offering of the Shares to the
     Selling  Stockholders and received a fee of $900,000 or approximately 4.75%
     of the aggregate  purchase  price and is entitled to  reimbursement  by the
     Company of travel,  legal and other out-of-pocket  expenses up to a maximum
     of $50,000.

(3)  Messrs.  Rothbaum  and Silber are  principals  with  Evolution  Capital,  a
     registered  broker-dealer which received a fee of $235,155 or approximately
     1.25% of the aggregate  purchase  price in connection  with the sale of the
     Shares to the Selling Stockholders. In February 1998, Evolution Capital was
     granted options to purchase 50,000 shares of the Company's  Common Stock at
     an exercise  price of $5.9375 per share pursuant to a one year advisory and
     consulting   agreement   which  requires   Evolution   Capital  to  provide
     institutional targeting,  dossier reports,  institutional  surveillance and
     overall  capital  markets  intelligence  to the Company.  In June 1996, The
     Carson Group Inc., an affiliate of Mr.  Rothbaum,  Mr. Silber and Evolution
     Capital,  received  $325,000  in cash  and  50,000  five-year  warrants  to
     purchase Common Stock at an exercise price of $4.11 per share as a finder's
     fee in  connection  with the Company's  private  placement of Common Stock,
     preferred  stock and warrants in January and March 1996.  In addition,  The
     Carson Group Inc. has received  approximately  $175,000 in consulting  fees
     during the past two years for providing  institutional  targeting,  dossier
     reports,   institutional   surveillance   and   overall   capital   markets
     intelligence to the Company.

     The Company has agreed to bear the  expenses  (other than broker  discounts
and  commissions,  if any, and expenses of counsel and other advisors to certain
of the Selling Stockholders) incurred in connection with the registration of the
Shares.

                              PLAN OF DISTRIBUTION

     The  Shares  may be  sold  pursuant  to  this  Prospectus  by  the  Selling
Stockholders.  These  sales  may  occur  from  time  to  time  in  one  or  more
transactions  (which may involve block  transactions)  in the open  markets,  in
negotiated  transactions,  through the writing of options on the Shares (whether
such options are listed on an options exchange or otherwise) or by a combination
of such methods of sale, at fixed prices which may be changed,  at market prices
prevailing at the time of sale, at prices related to prevailing market prices or
at negotiated prices. The Selling  Stockholders may effect these transactions by
selling the Shares to or through broker-dealers, who may receive compensation in
the form of discounts or commissions  from the Selling  Stockholders or from the
purchasers of the Shares for whom the broker-dealers may act as agent or to whom
they may sell as  principal,  or both in  amounts to be  negotiated  immediately
prior to the sale.  The  Selling  Stockholders  may also  pledge  the  Shares as
collateral for margin  accounts or loans and the Shares could be resold pursuant
to the terms of such  accounts  or loans.  There are  currently  no  agreements,
arrangements or understandings  with respect to the sale of any of the Shares by
the  Selling  Stockholders.  The Shares are being  registered  to permit  public
secondary  trading of the  Shares,  and the Selling  Stockholders  may offer the
Shares for resale from time to time. In effecting sales,  broker-dealers engaged
by the Selling Stockholders may arrange for other broker-dealers to participate.
Broker-dealers   will  receive   commissions   or  discounts  from  the  Selling
Stockholders in amounts to be negotiated  immediately prior to the sale. Neither
the Company nor the Selling  Stockholders  can presently  estimate the amount of
commissions or discounts,  if any, that will be paid by the Selling Stockholders
on account of their  sale of the  Shares  from time to time.  In order to comply
with the securities  laws of certain states,  if applicable,  the Shares will be
sold in such  jurisdictions  only  through  registered  or  licensed  brokers or
dealers.  In addition,  in certain states the Shares may not be sold unless they
have  been  registered  or  qualified  for  sale in the  applicable  state or an
exemption from the registration or qualification requirement is available and is
complied with by the Company and the Selling Stockholders.


                                       15
<PAGE>


     The Selling  Stockholders and any  broker-dealers who execute sales for the
Selling  Stockholders may be deemed to be  "underwriters"  within the meaning of
the  Securities Act by virtue of the number of shares of Common Stock to be sold
or resold by such persons or entities or the manner of sale thereof, or both. If
the Selling Stockholders,  broker-dealers or other holders were determined to be
underwriters,  any  discounts or  commissions  received by them or by brokers or
dealers acting on their behalf and any profits received by them on the resale of
their shares of Common Stock might be deemed underwriting compensation under the
Securities Act.

     The Selling  Stockholders have represented to the Company that any purchase
or sale of the Common Stock by them will be in compliance with applicable  rules
and regulations of the Commission.

     In addition,  any securities  covered by this Prospectus  which qualify for
sale  pursuant to Rule 144 under the  Securities  Act may be sold under Rule 144
rather than pursuant to this Prospectus.  To the extent  required,  the specific
shares  of  Common  Stock  to  be  sold,  the  name  of  any  successor  Selling
Stockholders,  the public offering price, the names of any such agent, dealer or
underwriter,  and any  applicable  commission  or discount  with  respect to any
particular offer will be set forth in an accompanying Prospectus Supplement. See
"Selling Stockholders."

     Under applicable  rules and regulations  under the Exchange Act, any person
engaged  in the  distribution  of the Shares  may not  simultaneously  engage in
market making  activities  with respect to the Common Stock of the Company for a
restricted  period prior to the commencement of such  distribution.  In addition
and without  limiting  the  foregoing,  the Selling  Stockholders  and any other
person participating in a distribution will be subject to applicable  provisions
of the Exchange Act and the rules and regulations thereunder, including, without
limitation, Regulation M, which provisions may limit the timing of purchases and
sales of shares of the Company's Common Stock by the Selling Stockholders.

     The  Company  has agreed to  indemnify  the  Selling  Stockholders  against
certain liabilities, including liabilities under the Securities Act. The Selling
Stockholders  have agreed to indemnify the Company against certain  liabilities,
including liabilities under the Securities Act.

     There can be no assurance  that the Selling  Stockholders  will sell all or
any of the Shares offered hereby.

                                  LEGAL MATTERS

     The legality of the shares of Common Stock  offered  hereby has been passed
on for the Company by Dorsey & Whitney LLP, New York, New York.

                                     EXPERTS

     The consolidated financial statements of Enzon, Inc. and subsidiaries as of
June 30, 1997 and 1996 and for each of the years in the three-year  period ended
June  30,  1997,  have  been   incorporated  by  reference  herein  and  in  the
Registration  Statement  in reliance  upon the report of KPMG Peat  Marwick LLP,
independent certified public accountants,  incorporated by reference herein, and
upon the authority of said firm as experts in accounting and auditing.


                                       16
<PAGE>


                                     PART II
                     INFORMATION NOT REQUIRED IN PROSPECTUS

Item 14. Other Expenses of Issuance and Distribution

     The  following  table sets forth an itemized  estimate of fees and expenses
(other than the Securities and Exchange  Commission  registration fee and Nasdaq
filing fee)  payable by the  Registrant  in  connection  with the  issuance  and
distribution of the securities described in this registration  statement,  other
than underwriting discounts and commissions.

SEC registration fee ........................................           $  6,500
Nasdaq filing fee ...........................................           $ 17,500
Legal fees and expenses .....................................           $ 90,000
Accounting fees and expenses ................................           $ 10,000
Placement agent expense reimbursement .......................           $ 50,000
Miscellaneous ...............................................           $ 10,000

     Total ..................................................           $184,000
                                                                        ========

Item 15. Indemnification of Directors and Officers

     The General  Corporation Law of the State of Delaware (the "DGCL") provides
for  indemnification  as set forth in  Section  145  thereof.  The  Registrant's
By-laws, as amended provide for indemnification of the directors and officers of
the Registrant against all costs,  expenses and amounts of liability incurred by
them in  connection  with any  action,  suit or  proceeding  in  which  they are
involved  by reason of their  affiliation  with the  Registrant,  to the fullest
extent  permitted  by law. The  Registrant's  directors  and officers  also have
indemnification agreements with the Registrant, which expand the indemnification
protection provided to them under the Registrant's By-laws.

     The Company's Certificate of Incorporation  provides that a director of the
Company will not be personally liable for monetary damages to the Company or its
stockholders  for breach of fiduciary duty as a director,  except for liability,
(i) for any breach of the director's duty of loyalty to such  corporation or its
stockholders,  (ii) for acts or  omissions  not in good  faith or which  involve
intentional  misconduct  or a  knowing  violation  of law,  (iii)  for  unlawful
payments of dividends or unlawful stock  repurchase or redemption as provided in
Section  174 of the DGCL or (iv) for any  transaction  from  which the  director
derived an improper personal benefit.

Item 16.  Exhibits
          --------

                                                                 Page Number
Exhibit                                                         or Incorporation
Number  Description                                              By Reference  
- ------  -----------                                              ------------  

1.1     Form of  Common Stock Purchase Agreement with Selling
        Stockholders                                                      E-1

4.1     Certificate of Incorporation, as amended                            *

4.2     Certificate of Amendment of Certificate of Incorporation         
        filed with the Delaware Secretary of State on
        January 5, 1998                                                   E-64

                                      II-1
<PAGE>



4.3     By-laws, as amended                                                **

5.1     Opinion of Dorsey & Whitney LLP regarding legality                E-66

23.1    Consent of Dorsey & Whitney LLP (contained
        in opinion filed as Exhibit 5.1)

23.2    Consent of KPMG Peat Marwick LLP                                  E-68

24.0    Power of Attorney 

*    Previously  filed as an exhibit to the Company's  Quarterly  Report on Form
     10-Q for the  quarter  ended  March  31,  1996 and  incorporated  herein by
     reference thereto.
**   Previously filed as an exhibit to the Company's  Registration  Statement on
     Form S-2 (File No. 33-34874) and incorporated herein by reference thereto.
***  Previously filed.

                                      II-2
<PAGE>


Item 17. Undertakings

The undersigned Registrant hereby undertakes:

     (1) To file,  during any period in which  offers or sales are being made, a
post-effective amendment to this registration statement:

     (i)  To  include  any  prospectus  required  by  Section  10(a)(3)  of  the
Securities Act of 1933;

     (ii) To reflect in the  prospectus  any facts or events  arising  after the
effective date of the registration  statement (or the most recent post-effective
amendment  thereof)  which,  individually  or  in  the  aggregate,  represent  a
fundamental  change in the information set forth in the registration  statement.
Notwithstanding the foregoing,  any increase or decrease in volume of securities
offered (if the total dollar value of  securities  offered would not exceed that
which  was  registered)  and any  deviation  from  the  low or  high  end of the
estimated  maximum  offering  range may be reflected  in the form of  prospectus
filed with the  Commission  pursuant  to Rule 424(b) if, in the  aggregate,  the
changes  in the  volume  and price  represent  no more than a 20%  change in the
maximum  aggregate  offering price set forth in the "Calculation of Registration
Fee" table in the effective registration statement.

     (iii) To  include  any  material  information  with  respect to the plan of
distribution  not  previously  disclosed  in the  registration  statement or any
material change to such information in the registration statement:

     Provided,  however,  that paragraphs (1)(i) and (1)(ii) do not apply if the
registration statement is on Form S-3, Form S-8 or Form F-3, and the information
required to be included in a  post-effective  amendment by those  paragraphs  is
contained in the periodic reports filed by the Registrant pursuant to Section 13
or Section 15(d) of the Securities Exchange Act of 1934 that are incorporated by
reference in the registration statement.

     (2) That, for the purpose of determining any liability under the Securities
Act of 1933,  each  such  post-effective  amendment  shall be deemed to be a new
registration  statement  relating to the  securities  offered  therein,  and the
offering of such  securities at that time shall be deemed to be the initial bona
fide offering thereof.

     (3) To remove from registration by means of a post-effective  amendment any
of the securities being registered which remain unsold at the termination of the
offering.

     (4) That,  for purposes of determining  any liability  under the Securities
Act of 1933, each filing of the  Registrant's  annual report pursuant to Section
13(a) or  Section  15(d)  of the  Securities  Exchange  Act of 1934  (and  where
applicable,  each filing of an employee benefit plan's annual report pursuant to
Section 15(d) of the Securities  Exchange Act of 1934) that is  incorporated  by
reference  in  this  Registration   Statement  shall  be  deemed  to  be  a  new
Registration  Statement  relating to the  securities  offered  therein,  and the
offering of such  securities at that time shall be deemed to be the initial bona
fide offering thereof.

     (5) Insofar as indemnification for liabilities arising under the Securities
Act of 1933 may be permitted to directors,  officers and controlling  persons of
the Registrant pursuant to the foregoing provisions or otherwise, the Registrant
has been advised that in the opinion of the Securities  and Exchange  Commission
such  indemnification  is against  public policy as expressed in the Act and is,
therefore,  unenforceable. In the event that a claim for indemnification against
such liabilities  (other than the payment by the Registrant of expenses incurred
or paid by a director,  officer or controlling  person of  the



                                      II-3
<PAGE>


Registrant  in the  successful  defense of any action,  suit or  proceeding)  is
asserted by such director,  officer or controlling person in connection with the
securities being  registered,  the Registrant will, unless in the opinion of its
counsel the matter has been settled by controlling precedent,  submit to a court
of appropriate  jurisdiction the question whether such  indemnification by it is
against  public policy as expressed in the Act and will be governed by the final
adjudication of such issue.


                                      II-4
<PAGE>


                                   SIGNATURES

     Pursuant to the  requirements of the Securities Act of 1933, the Registrant
certifies  that it has  reasonable  grounds to believe  that it meets all of the
requirements  for  filing  on Form S-3 and has  duly  caused  this  Registration
Statement  to be  signed  on its  behalf  by  the  undersigned,  thereunto  duly
authorized in the City of Piscataway, State of New Jersey, on July 9, 1998.

                                                      ENZON, INC.

                                                      By: /s/ Peter G. Tombros 
                                                          ----------------------
                                                          Peter G. Tombros,
                                                          President and Chief
                                                          Executive Officer


     Pursuant  to  the   requirements  of  the  Securities  Act  of  1933,  this
Registration  Statement  has  been  signed  by  the  following  persons  in  the
capacities and on the dates indicated.

    Signature                          Capacity                       Date

/s/Peter G. Tombros               President, Chief                 July 9, 1998
- ----------------------            Executive Officer and Director  
Peter G. Tombros                 (Principal Executive Officer)              
                                              

*                                 Chairman of the Board            July 9, 1998
- ---------------------- 
Randy H. Thurman


                                      II-5
<PAGE>



/s/ Kenneth J. Zuerblis          Vice President - Finance and      July 9, 1998
- -------------------------        Chief Financial Officer           
Kenneth J. Zuerblis              (Principal Financial Officer         
                                 and Principal Accounting Officer)      
                                              

*                                Director                          July 9, 1998
- -------------------------                                                 
Rosina B. Dixon

*                                Director                          July 9, 1998
- -------------------------                                                 
Robert LeBuhn

*                                Director                          July 9, 1998
- -------------------------                                                  
A.M. "Don" MacKinnon

*                                Director                          July 9, 1998
- -------------------------
Rolf A. Classon

*                                Director                          July 9, 1998
- -------------------------
David Golde


                                      II-6
<PAGE>


                                   ENZON, INC.

                                  EXHIBIT INDEX

Exhibit No.    Description

1.1            Form of Common Stock Purchase Agreement with Selling Stockholders

4.2            Certificate of Amendment of Certificate of Incorporation

5.1            Opinion of Dorsey & Whitney LLP regarding legality

23.1           Consent of Dorsey & Whitney LLP (contained in opinion filed as
               Exhibit 5.1)

23.2           Consent of KPMG Peat Marwick LLP



                                      II-7
<PAGE>


                         ==============================

                       SECURITIES AND EXCHANGE COMMISSION

                             WASHINGTON, D.C. 20549

                               ___________________

                                    EXHIBITS

                                       TO

                               AMENDMENT NO. 1 TO

                                    FORM S-3

                             REGISTRATION STATEMENT

                                      UNDER

                           THE SECURITIES ACT OF 1933

                               ___________________

                                   ENZON, INC.
             (Exact name of Registrant as specified in its charter)

                         ==============================





                         -------------------------------
                                   ENZON, INC.

                         COMMON STOCK PURCHASE AGREEMENT

                                  June 25, 1998
                          -------------------------------






<PAGE>



                                TABLE OF CONTENTS

                                                                            Page
                                                                            ----
Section 1

           Authorization and Sale of Common Stock .........................    1
  1.1  Authorization ......................................................    1
  1.2  Sale of Common .....................................................    1

Section 2

           Closing Date: Delivery .........................................    1
  2.1  Closing Date .......................................................    1
  2.2  Delivery ...........................................................    1

Section 3

           Representations and Warranties of the Company ..................    2
  3.1  Organization and Standing ..........................................    2
  3.2  Corporate Power, Authorization .....................................    2
  3.3  Issuance and Delivery of the Shares ................................    2
  3.4  Private Placement Offering Memorandum: SEC Documents, Financial
       Statements .........................................................    2
  3.5  Governmental Consents ..............................................    3
  3.6  No Material Adverse Change .........................................    3
  3.7  Intellectual Property ..............................................    3
  3.8  Authorized Capital Stock ...........................................    4
  3.9  Litigation .........................................................    4
  3.10 Use of Proceeds ....................................................    4
  3.11 Accountants ........................................................    4
  3.12 Compliance With Other Instruments ..................................    5
  3.13 Permits ............................................................    5
  3.14 Investment Company .................................................    5
  3.15 Offering Materials .................................................    5

Section 4

           Representations, Warranties and Covenants of the Purchasers ....    5
  4.1  Power; Authorization ...............................................    5
  4.2  Investment Experience ..............................................    6
  4.3  Investment Intent ..................................................    6
  4.4  Registration or Exemption Requirements .............................    6



                                      E-1
<PAGE>


                                TABLE OF CONTENTS
                                   (continued)


Section 5

           Conditions to Closing of Purchasers ............................    6
  5.1  Representations and Warranties .....................................    7
  5.2  Covenants ..........................................................    7
  5.3  Blue Sky ...........................................................    7
  5.4  Legal Opinion ......................................................    7
  5.5  Patent Opinion .....................................................    7
  5.6  Registration Statement .............................................    7
  5.7  Nasdaq Qualification ...............................................    7

Section 6

           Conditions to Closing of Company ...............................    7
  6.1  Representations and Warranties .....................................    8
  6.2  Covenants ..........................................................    8
  6.3  Blue Sky ...........................................................    8
  6.4  Registration Statement .............................................    8
  6.5  Nasdaq Qualification ...............................................    8

Section 7

           Affirmative Covenants of the Company ...........................    8
  7.1  Financial Information ..............................................    8
  7.2  Registration Requirements ..........................................    8
  7.3  Indemnification and Contribution ...................................   10

Section 8

           Restrictions on Transferability of Shares:
           Compliance with Securities Act .................................   12
  8.1  Restrictions on Transferability ....................................   13
  8.2  Restrictive Legend .................................................   13
  8.3  Transfer of Shares After Registration ..............................   13
  8.4  Purchaser Information ..............................................   13

Section 9

           Miscellaneous ..................................................   14
  9.1  Waivers and Amendments .............................................   14


                                      E-2
<PAGE>


                                TABLE OF CONTENTS
                                   (continued)


  9.2  Placement Agent Fee ................................................  14
  9.3  Governing Law ......................................................  14
  9.4  Survival ...........................................................  14
  9.5  Successors and Assigns .............................................  14
  9.6  Entire Agreement ...................................................  14
  9.7  Notices, etc .......................................................  14
  9.8  Severability of this Agreement .....................................  15
  9.9  Counterparts .......................................................  15
  9.10 Further Assurances .................................................  15
  9.11 Termination ........................................................  15
  9.12 Expenses ...........................................................  15
  9.13 Currency ...........................................................  15
                                                                      
Exhibit A - Schedule of Purchasers
Exhibit B - Form of Purchaser's Questionnaire
Exhibit C - Opinion of Company  Counsel 
Exhibit D - Opinions of Patent  Counsel
Exhibit E - Form of Purchaser's Legend Removal Certificate
Exhibit F - Form of Purchaser's Certificate of Subsequent Sale
Exhibit G - Description of Capital Stock









                                      E-3
<PAGE>

                                   ENZON, INC.


                         COMMON STOCK PURCHASE AGREEMENT

     This Common Stock Purchase  Agreement (the  "Agreement") is made as of June
25, 1998, by and among Enzon, Inc., a Delaware corporation (the "Company"), with
its principal office at 20 Kingsbridge  Road,  Piscataway,  New Jersey,  and the
persons  listed on the Schedule of Investors  attached  hereto as Exhibit A (the
"Purchasers").

                                    Section 1

                     Authorization and Sale of Common Stock

     1.1  Authorization.  The Company has  authorized  the sale and  issuance of
3,985,000  shares of its Common  Stock,  $0.01 par value per share (the  "Common
Stock") pursuant to this Agreement (the "Shares").

     1.2 Sale of Common.  Subject to the terms and conditions of this Agreement,
the  Company  agrees  to issue  and sell to each  Purchaser  and each  Purchaser
severally  agrees to  purchase  from the  Company the number of Shares set forth
opposite such Purchaser's name on Exhibit A for $4.75 per share.

                                    Section 2

                             Closing Date: Delivery

     2.1  Closing  Date.  The  closing  of the  purchase  and sale of the Shares
hereunder (the "Closing")  shall be held at the offices of Dorsey & Whitney LLP,
250 Park Avenue,  New York, NY 10177,  at or before 10:00 a.m. New York Time, on
that date that is two  business  days  after the date on which the  Registration
Statement  (as defined  herein) is declared  effective or at such time and place
upon which the Company and SBC Warburg Dillon Read Inc. (the "Placement  Agent")
shall agree. The date of the Closing is hereinafter  referred to as the "Closing
Date."

     2.2 Delivery.  At the Closing, the Company will deliver to each Purchaser a
certificate,  registered  in  the  Purchaser's  name  as  shown  on  Exhibit  A,
representing  the  number of  Shares  to be  purchased  by the  Purchaser.  Such
delivery  shall be  against  payment  of the  purchase  price  therefor  by wire
transfer to the Company's bank account in the amount set forth on Exhibit A.





                                      E-4
<PAGE>



                                    Section 3

                  Representations and Warranties of the Company

     The Company  represents  and warrants to the  Purchasers  as of the Closing
Date as follows:

     3.1 Organization and Standing.  The Company is a corporation duly organized
and validly  existing under, and by virtue of, the laws of the State of Delaware
and is in good standing as a domestic  corporation  under the laws of said state
and has all requisite  corporate  power and authority to conduct its business as
currently conducted and disclosed in the Offering Memorandum (as defined below).

     3.2 Corporate Power, Authorization. The Company has all requisite legal and
corporate  power and has taken all  requisite  corporate  action to execute  and
deliver  this  Agreement,  to sell and  issue  the  Shares  and to carry out and
perform all of its obligations under this Agreement.  This Agreement constitutes
the  legal,  valid  and  binding  obligation  of  the  Company,  enforceable  in
accordance  with its terms,  except (i) as  limited  by  applicable  bankruptcy,
insolvency,  reorganization  or  similar  laws  relating  to  or  affecting  the
enforcement  of  creditors'  rights  generally  and (ii) as limited by equitable
principles generally. The execution and delivery of this Agreement does not, and
the performance of this Agreement and the compliance with the provisions  hereof
and the  issuance,  sale and  delivery  of the Shares by the  Company  will not,
conflict  with or result in a breach or  violation of the terms,  conditions  or
provisions  of, or  constitute  a default  under,  or result in the  creation or
imposition  of  any  lien  pursuant  to  the  terms  of,  the   Certificate   of
Incorporation  or Bylaws of the Company or any statute,  law, rule or regulation
or any state or federal order,  judgment or decree or any  indenture,  mortgage,
lease or other  agreement  or  instrument  to which  the  Company  or any of its
properties is subject.

     3.3  Issuance  and  Delivery  of the  Shares.  The  Shares,  when issued in
compliance with the provisions of this Agreement,  will be validly issued, fully
paid and  nonassessable.  The issuance and delivery of the Shares is not subject
to preemptive or any other similar rights of the  stockholders of the Company or
any liens or encumbrances.

     3.4  Private  Placement  Offering  Memorandum:  SEC  Documents,   Financial
Statements.  Each  complete or partial  statement,  report,  or proxy  statement
included within the Company's Private Placement  Offering  Memorandum dated June
4, 1998 (the  "Offering  Memorandum")  is a true and complete copy of or excerpt
from such  document as filed by the Company  with the  Securities  and  Exchange
Commission  (the "SEC").  The Company has filed in a timely manner all documents
that the Company was required to file with the SEC under  Sections 13, 14(a) and
15(d) of the Securities  Exchange Act of 1934, as amended (the "Exchange  Act"),
during the twelve (12) months preceding the date of this Agreement.  As of their
respective  filing dates,  all documents  filed by the Company with the SEC (the
"SEC Documents")  complied in all material respects with the requirements of the
Exchange Act or the



                                      E-5
<PAGE>



Securities  Act of 1933,  as amended  (the  "Securities  Act"),  as  applicable.
Neither  the  Offering  Memorandum  nor any of the  SEC  Documents  as of  their
respective  dates contained any untrue  statement of material fact or omitted to
state a material  fact  required to be stated  therein or  necessary to make the
statements  made therein,  in light of the  circumstances  under which they were
made,  not  misleading.  As of their  respective  filing  dates,  the  financial
statements  of  the  Company  included  in the  SEC  Documents  (the  "Financial
Statements")  complied  as to  form in all  material  respects  with  applicable
accounting  requirements and with the published rules and regulations of the SEC
with respect thereto.  The Financial Statements have been prepared in accordance
with generally accepted accounting  principles  consistently  applied and fairly
present the consolidated  financial position of the Company and any subsidiaries
at the dates  thereof  and the  consolidated  results  of their  operations  and
consolidated cash flows for the periods then ended; provided,  however, that the
unaudited  Financial   Statements  are  subject  to  normal  recurring  year-end
adjustments  (which in any case will not be  material)  and do not  contain  all
footnotes required under generally accepted accounting principles.

     3.5 Governmental Consents. No consent, approval, order or authorization of,
or  registration,  qualification,  designation,  declaration or filing with, any
federal,  state, or local  governmental  authority on the part of the Company is
required in connection with the consummation of the transactions contemplated by
this Agreement  except for (a) compliance  with the securities and blue sky laws
in the states in which  Shares are offered  and/or  sold,  (b) the filing of the
Registration  Statement and all amendments  thereto with the SEC as contemplated
by Section 7.2 of this  Agreement  and (c) all required  filings with The Nasdaq
Stock Market necessary for the listing of the Shares.

     3.6 No  Material  Adverse  Change.  Except as  otherwise  disclosed  in the
Offering  Memorandum,  since March 31, 1998,  there have not been any changes in
the assets,  liabilities,  financial condition or operations of the Company from
those  reflected in the  Financial  Statements,  except  changes in the ordinary
course of business which have not been, either individually or in the aggregate,
materially adverse.

     3.7 Intellectual Property.  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



                                      E-6
<PAGE>



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.

     3.8 Authorized  Capital Stock.  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 hereto;  there is no capital
stock  outstanding as of such dates other than as described in Exhibit G hereto;
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.  Except
as disclosed in or  contemplated  by the Offering  Memorandum  and the Financial
Statements and the related notes thereto included in the Offering  Memorandum or
in  Exhibit G hereto,  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.  Except as described in Exhibit G
hereto, 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 Securities Act in the Registration Statement.

     3.9 Litigation.  Except as set forth in the Offering Memorandum,  there are
no actions, suits,  proceedings or investigations pending or, to the best of the
Company's  knowledge,  threatened  against the Company or any of its  properties
before  or by any  court or  arbitrator  or any  governmental  body,  agency  or
official in which there is the possibility of an adverse decision that (a) would
reasonably  be  expected  to have a  material  adverse  effect on the  Company's
properties  or assets or the business of the Company as  presently  conducted or
proposed  to be  conducted  or (b) would  reasonably  be  expected to impair the
ability of the Company to perform its obligations under this Agreement.

     3.10 Use of Proceeds. The Company will apply the net proceeds from the sale
of the Shares in the manner set forth under the caption "Use of Proceeds" in the
Offering Memorandum.

     3.11  Accountants.  KPMG Peat Marwick LLP, who have expressed their opinion
with respect to the audited financial  statements and schedules to be filed with
the SEC as a part of the Registration Statement and included in the Registration
Statement  and the  Prospectus  which  forms  a part  thereof,  are  independent
accountants  as required  by the  Securities  Act and the rules and  regulations
promulgated thereunder (the "Rules and Regulations").




                                      E-7
<PAGE>



     3.12 Compliance With Other Instruments.  Except as to defaults,  violations
and breaches which individually or in the aggregate would not be material to the
Company,  the Company is not in  violation  or default of any  provision  of its
Articles  of  Incorporation  or  Bylaws,  each as  amended  to  date,  or of any
agreement, license, permit, instrument, judgment, order, writ or decree to which
it is a party or by which it is bound, or, to the best of its knowledge,  of any
provision of any federal or state statute,  rule or regulation applicable to the
Company.

     3.13 Permits. The Company has all franchises,  permits,  licenses,  and any
similar  authority  necessary  for the  conduct  of its  business  as now  being
conducted by it, the lack of which could  materially  and  adversely  affect the
business,  properties,  prospects,  or financial  condition of the Company.  The
Company is not in default in any material  respect under any of such franchises,
permits, licenses, or other similar authority.

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

     3.15  Offering  Materials.  The  Company has not  distributed  and will not
distribute  prior to the Closing Date any offering  material in connection  with
the offering and sale of the Shares other than the Offering Memorandum.

                                    Section 4

           Representations, Warranties and Covenants of the Purchasers

     Each  Purchaser  hereby  severally  represents and warrants to the Company,
effective as of the Closing Date, as follows:

     4.1 Power;  Authorization.  (i) Such Purchaser has all requisite  legal and
corporate or other power and capacity and has taken all  requisite  corporate or
other action to execute and deliver this Agreement, to purchase the Shares to be
purchased by it and to carry out and perform all of its  obligations  under this
Agreement;  and (ii) this  Agreement  constitutes  the legal,  valid and binding
obligation of such Purchaser,  enforceable in accordance with its terms,  except
(a) as limited by applicable bankruptcy, insolvency,  reorganization, or similar
laws relating to or affecting the enforcement of creditors' rights generally and
(b) as limited by equitable principles generally.

     4.2 Investment  Experience.  Such Purchaser is an "accredited  investor" as
defined in Rule 501(a) under the Securities Act. Such Purchaser has received and
reviewed the Offering Memorandum, is aware of the Company's business affairs and
financial   condition  and  has  had  access  to  and  has  acquired  sufficient
information about the Company to reach an informed and knowledgeable decision to
acquire the Shares.  Purchaser has such business and financial  experience as is
required  to permit it to  protect  its own  interests  in  connection  with the
purchase of the Shares.



                                      E-8
<PAGE>




     4.3  Investment  Intent.  Such  Purchaser is  purchasing  the Shares in the
ordinary course of its business for its own account as principal, for investment
purposes only,  and not with a present view to, or for, the resale  distribution
thereof,  in whole or in part,  within the meaning of the  Securities Act or any
state securities laws. Purchaser  understands that its acquisition of the Shares
has not been  registered  under the  Securities  Act or  registered or qualified
under  any  state  law in  reliance  on  specific  exemptions  therefrom,  which
exemptions  may depend upon,  among other  things,  the bona fide nature of such
Purchaser's  investment intent as expressed herein. Such Purchaser has completed
or caused to be completed the Purchaser Questionnaire attached hereto as Exhibit
B for use in preparation of the Registration  Statement (as defined below),  and
the  responses  provided  therein  shall be true and correct as of the effective
date of the Registration Statement and as of the Closing Date. Purchaser has, in
connection  with its  decision  to  purchase  the  number of Shares set forth in
Exhibit A hereto,  relied solely upon the Offering  Memorandum and the documents
attached as appendices  thereto and the  representations  and  warranties of the
Company  contained  herein.  Such  Purchaser  will not,  directly or indirectly,
offer, sell, pledge,  transfer or otherwise dispose of (or solicit any offers to
buy, purchase or otherwise acquire or take a pledge of) any of the Shares except
in compliance with the Securities Act, and the rules and regulations promulgated
thereunder and applicable state securities laws.

     4.4  Registration  or  Exemption   Requirements.   Such  Purchaser  further
acknowledges,  understands  and  agrees  that the  Shares  may not be  resold or
otherwise  transferred  except in a transaction  registered under the Securities
Act or unless an exemption from such  registration is available.  Such Purchaser
understands that the certificate(s) evidencing the Shares will be imprinted with
a  legend  that  prohibits  the  transfer  of the  Shares  unless  (i)  they are
registered or such  registration  is not  required,  and (ii) if the transfer is
pursuant  to an  exemption  from  registration  other  than  Rule 144  under the
Securities  Act and, if the Company  shall so request in writing,  an opinion of
counsel  reasonably  satisfactory  to the Company is obtained to the effect that
the transaction is so exempt.

                                    Section 5

                       Conditions to Closing of Purchasers

     Each  Purchaser's  obligation  to purchase the Shares at the Closing is, at
the option of such  Purchaser,  subject to the  fulfillment  or waiver as of the
Closing Date of the following conditions:

     5.1 Representations and Warranties. The representations and warranties made
by the  Company in Section 3 hereof  shall be true and  correct in all  material
respects  when made,  and shall be true and correct in all material  respects on
the Closing  Date with the same force and effect as if they had been made on and
as of said date.




                                      E-9
<PAGE>



     5.2 Covenants.  All covenants,  agreements and conditions contained in this
Agreement  to be  performed by the Company on or prior to the Closing Date shall
have been performed or complied with in all respects.

     5.3 Blue Sky. The Company shall have  obtained all  necessary  blue sky law
permits and  qualifications,  or secured exemptions  therefrom,  required by any
state or foreign or other jurisdiction for the offer and sale of the Shares.

     5.4 Legal Opinion.  The  Purchasers  shall have received a legal opinion of
Dorsey & Whitney LLP,  counsel to the  Company,  with respect to the matters set
forth on Exhibit C.

     5.5 Patent  Opinion.  The Purchasers  shall have received legal opinions of
patent  counsel to the Company  with respect to the matters set forth on Exhibit
D.

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

     5.7 Nasdaq  Qualification.  The Shares shall be duly authorized for listing
by the Nasdaq Stock Market.

                                    Section 6

                        Conditions to Closing of Company

     The Company's obligation to sell and issue the Shares at the Closing is, at
the option of the Company, subject to the fulfillment or waiver of the following
conditions:

     6.1  Representations  and  Warranties.  The  representations  made  by  the
Purchasers  in  Section  4  hereof  shall be true and  correct  in all  material
respects  when made,  and shall be true and correct in all material  respects on
the Closing  Date with the same force and effect as if they had been made on and
as of such date.

     6.2 Covenants.  All covenants,  agreements and conditions contained in this
Agreement  to be  performed  by the  Purchasers  on or prior to the Closing Date
shall have been performed or complied with in all material respects.

     6.3 Blue Sky. The Company shall have  obtained all  necessary  blue sky law
permits and  qualifications,  or secured exemptions  therefrom,  required by any
state for the offer and sale of the Shares.




                                      E-10
<PAGE>



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

     6.5 Nasdaq  Qualification.  The Shares shall be duly authorized for listing
by the Nasdaq Stock Market.

                                    Section 7

                      Affirmative Covenants of the Company

     The Company hereby covenants and agrees as follows:

     7.1 Financial  Information.  The Company will mail the following reports to
each  Purchaser  until  such  Purchaser  transfers,  assigns or sells the Shares
purchased by such Purchaser pursuant to this Agreement:

          (a) Within one hundred (100) days after the end of each fiscal year, a
     copy of its Annual Report on Form 10-K.

          (b) Within fifty-five (55) days after the end of the first, second and
     third quarterly  accounting  periods of each fiscal year of the Company,  a
     copy of its Quarterly Report on Form 10-Q.

          (c) Within ten (10) days after the Company files any Current Report on
     Form 8-K with the SEC, such Current Report on Form 8-K

     7.2 Registration Requirements.

          (a) The  Company  shall use its best  efforts  to  prepare  and file a
     registration  statement  with the SEC under the  Securities Act to register
     the resale of the Shares by the Purchasers (the  "Registration  Statement")
     no later than ten (10) days after the date hereof.

          (b) The Company shall pay all Registration Expenses (as defined below)
     in connection with any registration, qualification or compliance hereunder,
     and each  Purchaser  shall pay all Selling  Expenses (as defined below) and
     other expenses that are not  Registration  Expenses  relating to the Shares
     resold by such  Purchaser.  Registration  Expenses shall mean all expenses,
     except for Selling Expenses,  incurred by the Company in complying with the
     registration  provisions herein described,  including,  without limitation,
     all registration,  qualification and filing fees, printing expenses, escrow
     fees, fees and disbursements of counsel for the Company,  blue sky fees and
     expenses,  and the expense of any special audits incident to or required by
     any such registration. Selling Expenses shall mean all selling commissions,



                                      E-11
<PAGE>



     underwriting fees and stock transfer taxes applicable to the Shares and all
     fees and disbursements of counsel for any Purchaser.

          (c) In the case of the  registration  effected by the Company pursuant
     to these registration provisions,  the Company will use its reasonable best
     efforts to: (i) cause the Registration Statement to become effective within
     sixty (60) days of the date hereof,  (ii) keep such registration  effective
     until the earlier of (a) the second  anniversary  of the Closing Date,  (b)
     such date as all of the Shares have been resold by the original  Purchasers
     thereof,  or (c) such time as all of the Shares held by the  Purchasers can
     be sold  within a given  three-month  period  without  compliance  with the
     registration  requirements of the Securities Act pursuant to Rule 144 under
     the Securities Act; (iii) prepare and file with the SEC such amendments and
     supplements  to the  Registration  Statement  and  the  prospectus  used in
     connection  with the  Registration  Statement as may be necessary to comply
     with the provisions of the  Securities Act with respect to the  disposition
     of all securities covered by the Registration Statement;  (iv) furnish such
     number of prospectuses and other documents incident thereto,  including any
     amendment of or supplement to the  prospectus,  as a Purchaser from time to
     time may reasonably  request;  (v) cause all Shares registered as described
     herein  to be  listed  on  each  securities  exchange  and  quoted  on each
     quotation  service on which  similar  securities  issued by the Company are
     then listed or quoted;  (vi) provide a transfer agent and registrar for all
     Shares registered pursuant to the Registration Statement and a CUSIP number
     for all such Shares;  (vii)  otherwise  use its best efforts to comply with
     all  applicable  rules and  regulations  of the SEC;  and  (viii)  file the
     documents  required of the Company and  otherwise  use its best  efforts to
     maintain requisite blue sky clearance in (A) all jurisdictions in which any
     of the  Shares  are  originally  sold and (B) all other  states  reasonably
     specified  in writing by a Purchaser,  provided as to clause (B),  however,
     that in no event shall the Company be required to qualify to do business or
     consent  to  service  of  process  in any  state  in which it is not now so
     qualified or has not so consented.

          (d) The  Company  shall  furnish  to each  Purchaser  upon  request  a
     reasonable  number of copies of a  supplement  to or an  amendment  of such
     prospectus  as may be necessary in order to  facilitate  the public sale or
     other disposition of all or any of the Shares held by such Purchaser.

          (e) With a view to making  available to the Purchasers the benefits of
     Rule 144  promulgated  under the  Securities Act ("Rule 144") and any other
     rule or  regulation  of the SEC that may at any time permit a Purchaser  to
     sell  Shares  to  the  public  without   registration   or  pursuant  to  a
     registration on Form S-3, the Company covenants and agrees to: (i) make and
     keep  public  information  available,  as those  terms are  understood  and
     defined in Rule 144 under the Securities  Act, until the earlier of (A) the
     second  anniversary  of the  Closing  Date or (B)  such  date as all of the
     Shares shall have been resold by the original Purchasers thereof; (ii) file
     with the SEC in a timely manner all reports and other documents required of
     the  Company  under the  Securities  Act and the  Exchange  Act;  and (iii)
     furnish to any Purchaser  upon request,  as long as the Purchaser  owns any
     Shares,  (A) a written  statement by the Company that it has complied  with
     the reporting  requirements of the Securities Act and the Exchange Act, (B)
     a copy of the most recent annual or quarterly report of the Company, and



                                      E-12
<PAGE>



     (C) such other information as may be reasonably requested in order to avail
     any Purchaser of any rule or regulation of the SEC that permits the selling
     of any such Shares without registration or pursuant to such Form S-3.

          (f) At any time the Company may refuse to permit a Purchaser to resell
     any Shares pursuant to the Registration Statement;  provided, however, that
     in order to exercise this right,  the Company must deliver a certificate in
     writing to the  Purchasers  and the  Placement  Agent to the effect  that a
     cessation  of  the  ability  to  sell  under,  or  a  withdrawal  of,  such
     Registration  Statement  is  necessary  because  a  sale  pursuant  to  the
     Registration   Statement  in  its  then-current  form  would  constitute  a
     violation of the federal  securities  laws.  In such an event,  the Company
     shall use its best efforts to promptly amend the Registration  Statement if
     necessary and take all other actions necessary to allow such sale under the
     federal  securities laws, and shall notify the Purchasers and the Placement
     Agent  promptly  after  it  has  determined   that  such  sale  has  become
     permissible  under  the  federal  securities  laws.   Notwithstanding   the
     foregoing,  the Company  shall not under any  circumstances  be entitled to
     exercise its right to withdraw the registration statement more then one (1)
     time in any twelve  (12) month  period,  and the period  during  which such
     Registration  Statement may be withdrawn  shall not exceed sixty (60) days.
     Each Purchaser hereby covenants and agrees that it will not sell any Shares
     pursuant to the Registration  Statement during the periods the Registration
     Statement is withdrawn  or the ability to sell  thereunder  is suspended as
     set forth in this Section 7.2(f).

     7.3 Indemnification and Contribution.

          (a) The Company  agrees to indemnify and hold harmless each  Purchaser
     from and against any losses,  claims, damages or liabilities (or actions or
     proceedings in respect  thereof) to which such Purchaser may become subject
     (under the  Securities  Act or otherwise)  insofar as such losses,  claims,
     damages or liabilities (or actions or proceedings in respect thereof) arise
     out of or are based upon, any untrue statement of a material fact contained
     in the Registration  Statement, on the effective date thereof, or arise out
     of any failure by the Company to fulfill  any  undertaking  included in the
     Registration Statement,  and the Company will, as incurred,  reimburse such
     Purchaser  for  any  legal  or  other  expenses   reasonably   incurred  in
     investigating, defending or preparing to defend any such action, proceeding
     or claim;  provided,  however,  that the Company shall not be liable in any
     such case to the extent that such loss,  claim,  damage or liability arises
     out of or is based upon (i) an untrue  statement made in such  Registration
     Statement  in reliance  upon and in  conformity  with  written  information
     furnished to the Company by or on behalf of such Purchaser specifically for
     use in preparation of the Registration Statement,  (ii) the failure of such
     Purchaser to comply with the covenants and agreements  contained in Section
     8.3  hereof,  or (iii)  any  untrue  statement  in any  Prospectus  that is
     corrected in any subsequent  Prospectus that was delivered to the Purchaser
     prior to the pertinent sale or sales by the Purchaser.

          (b) Each Purchaser, severally and not jointly, agrees to indemnify and
     hold harmless the Company from and against any losses,  claims,  damages or
     liabilities  (or actions or  proceedings  in respect  thereof) to which the
     Company may become subject (under the


                                      E-13
<PAGE>


     Securities  Act or otherwise)  insofar as such losses,  claims,  damages or
     liabilities (or actions or proceedings in respect  thereof) arise out of or
     are based upon (i) an untrue statement made in such Registration  Statement
     in reliance upon and in conformity  with written  information  furnished to
     the  Company  by or on behalf  of such  Purchaser  specifically  for use in
     preparation  of the  Registration  Statement,  provided,  however,  that no
     Purchaser  shall be  liable  in any  such  case  for any  untrue  statement
     included in any Prospectus which statement has been corrected,  in writing,
     by such  Purchaser and delivered to the Company  before the sale from which
     such loss  occurred,  (ii) the failure of such Purchaser to comply with the
     covenants  and  agreements  contained  in Section 8.3 hereof,  or (iii) any
     untrue  statement in any  prospectus  that is  corrected in any  subsequent
     Prospectus  that was delivered to the Purchaser prior to the pertinent sale
     or sales by the Purchaser,  and each Purchaser,  severally and not jointly,
     will, as incurred,  reimburse  the Company for any legal or other  expenses
     reasonably incurred in investigating,  defending or preparing to defend any
     such action, proceeding or claim.

          (c) Promptly after receipt by any indemnified  person of a notice of a
     claim or the beginning of any action in respect of which indemnity is to be
     sought against an  indemnifying  person  pursuant to this Section 7.3, such
     indemnified person shall notify the indemnifying  person in writing of such
     claim or of the commencement of such action, and, subject to the provisions
     hereinafter  stated,  in case any such action  shall be brought  against an
     indemnified  person and the  indemnifying  person shall have been  notified
     thereof,  the indemnifying person shall be entitled to participate therein,
     and, to the extent that it shall wish, to assume the defense thereof,  with
     counsel  reasonably  satisfactory to the indemnified  person.  After notice
     from the indemnifying person to such indemnified person of the indemnifying
     person's  election to assume the defense thereof,  the indemnifying  person
     shall not be  liable  to such  indemnified  person  for any legal  expenses
     subsequently  incurred by such  indemnified  person in connection  with the
     defense thereof,  provided,  however, that if there exists or shall exist a
     conflict of interest  that would make it  inappropriate  in the  reasonable
     judgment of the  indemnified  person for the same counsel to represent both
     the  indemnified  person and such  indemnifying  person or any affiliate or
     associate  thereof,  the indemnified person shall be entitled to retain its
     own counsel at the expense of such indemnifying person.

          (d)  If  the  indemnification  provided  for in  this  Section  7.3 is
     unavailable to or insufficient to hold harmless an indemnified  party under
     subsection  (a) or (b) above in respect of any losses,  claims,  damages or
     liabilities  (or actions or  proceedings  in respect  thereof)  referred to
     therein,  then each indemnifying  party shall contribute to the amount paid
     or  payable by such  indemnified  party as result of such  losses,  claims,
     damages or liabilities  (or actions in respect  thereof) in such proportion
     as is  appropriate  to reflect the relative fault of the Company on the one
     hand and the  Purchasers on the other in connection  with the statements or
     omissions which resulted in such losses, claims, damages or liabilities (or
     actions  in  respect  thereof),  as well as any  other  relevant  equitable
     considerations.  The relative  fault shall be  determined  by reference to,
     among other  things,  whether the untrue or alleged  untrue  statement of a
     material fact or the omission or alleged  omission to state a material fact
     relates  to  information  supplied  by the  Company  on the  one  hand or a
     Purchaser on the other and the parties' relative intent, knowledge,  access
     to information and opportunity to correct or prevent such statement or



                                      E-14
<PAGE>



     omission.  The Company and the  Purchasers  agree that it would not be just
     and  equitable  if  contribution  pursuant  to  this  subsection  (d)  were
     determined by pro rata  allocation  (even if the Purchasers were treated as
     one entity for such  purpose) or by any other  method of  allocation  which
     does not take account of the equitable  considerations referred to above in
     this subsection (d). The amount paid or payable by an indemnified  party as
     a result of the  losses,  claim,  damages,  or  liabilities  (or actions in
     respect  thereof)  referred to above in this subsection (d) shall be deemed
     to  include  any  legal  or  other  expenses  reasonably  incurred  by such
     indemnified  party in connection with  investigating  or defending any such
     action or claim.  Notwithstanding the provisions of this subsection (d), no
     Purchaser  shall be  required  to  contribute  any  amount in excess of the
     amount by which the net amount  received by the Purchaser  from the sale of
     the Shares to which such loss  relates  exceeds  the amount of any  damages
     which such  Purchaser has otherwise  been required to pay by reason of such
     untrue or alleged  untrue  statement  or omission or alleged  omission.  No
     person  guilty of  fraudulent  misrepresentation  (within  the  meaning  of
     Section 11(f) of the Securities Act) shall be entitled to contribution from
     any  person who was not guilty of such  fraudulent  misrepresentation.  The
     Purchasers' obligations in this subsection (d) to contribute are several in
     proportion to their  respective  sales of Shares to which such loss relates
     and not joint.

          (e) The  obligations  of the  Company  and the  Purchasers  under this
     Section 7.3 shall be in addition to any liability which the Company and the
     respective  Purchasers may otherwise  have and shall extend,  upon the same
     terms and conditions,  to each person,  if any, who controls the Company or
     any Purchaser within the meaning of the Act.

                                    Section 8

                   Restrictions on Transferability of Shares:
                          Compliance with Securities Act

     8.1 Restrictions on  Transferability.  The Shares shall not be transferable
in the  absence  of a  registration  under the  Securities  Act or an  exemption
therefrom or in the absence of compliance with any term of this  Agreement.  The
Company  shall be entitled to give stop  transfer  instructions  to its transfer
agent with respect to the Shares in order to enforce the foregoing restrictions.

     8.2 Restrictive  Legend.  Each certificate  representing  Shares shall bear
substantially  the following  legends (in addition to any legends required under
applicable securities laws):

               THE SHARES  REPRESENTED  BY THIS  CERTIFICATE
               HAVE BEEN  ACQUIRED FOR  INVESTMENT  PURPOSES
               ONLY AND HAVE NOT BEEN  REGISTERED  UNDER THE
               SECURITIES ACT OF 1933. THE SHARES MAY NOT BE
               SOLD OR  TRANSFERRED  IN THE  ABSENCE OF SUCH
               REGISTRATION OR AN EXEMPTION THEREFROM.



                                      E-15
<PAGE>


               ADDITIONALLY   THE  TRANSFER  OF  THE  SHARES
               REPRESENTED BY THIS CERTIFICATE IS SUBJECT TO
               CERTAIN RESTRICTIONS  SPECIFIED IN THE COMMON
               STOCK PURCHASE  AGREEMENT DATED JUNE 25, 1998
               BETWEEN   THE   COMPANY   AND  THE   ORIGINAL
               PURCHASER, AND NO TRANSFER OF SHARES SHALL BE
               VALID OR  EFFECTIVE  ABSENT  COMPLIANCE  WITH
               SUCH RESTRICTIONS.  ALL SUBSEQUENT HOLDERS OF
               THIS CERTIFICATE WILL HAVE AGREED TO BE BOUND
               BY  CERTAIN  OF THE  TERMS OF THE  AGREEMENT,
               INCLUDING   SECTIONS   7.2  AND  8.3  OF  THE
               AGREEMENT.  COPIES  OF THE  AGREEMENT  MAY BE
               OBTAINED AT NO COST BY WRITTEN  REQUEST  MADE
               BY THE REGISTERED  HOLDER OF THIS CERTIFICATE
               TO THE SECRETARY OF THE COMPANY.

     The legend  contained in this Section 8.2 may be removed from a certificate
either in  accordance  with  Section  8.3 or  immediately  upon  receipt  by the
Transfer  Agent of a certificate  substantially  in the form attached  hereto as
Exhibit E.

     8.3 Transfer of Shares After Registration.  Each Purchaser hereby covenants
with the  Company  not to make  any  sale of the  Shares  except  either  (i) in
accordance with the Registration Statement, in which case Purchaser covenants to
comply with the  requirement  of  delivering  a current  prospectus,  or (ii) in
accordance with Rule 144, in which case Purchaser  covenants to comply with Rule
144.  Purchaser  further  acknowledges  and  agrees  that  such  Shares  are not
transferable on the books of the Company unless the certificate submitted to the
Company's  transfer  agent  evidencing  such Shares is accompanied by a separate
certificate  executed by an officer of, or other person duly  authorized by, the
Purchaser in the form attached hereto as Exhibit F.

     8.4 Purchaser  Information.  Each Purchaser covenants that it will promptly
notify  the  Company  of  any  changes  in  the  information  set  forth  in the
Registration  Statement  regarding such Purchaser or such  Purchaser's  "Plan of
Distribution."

                                    Section 9

                                  Miscellaneous

     9.1 Waivers and  Amendments.  With the  exception  of Sections  7.1 and 7.2
hereof,  the terms of this  Agreement  may be waived or amended with the written
consent of the Company and each Purchaser.  With respect to Sections 7.1 and 7.2
hereof,  with the written  consent of the Company and the record holders of more
than fifty percent (50%) of the Shares then  outstanding and held by Purchasers,
the terms of the Agreement may be waived or amended



                                      E-16
<PAGE>



and any such  amendment  or waiver  shall be binding  upon the  Company  and all
holders of Shares.

     9.2  Placement  Agent Fee.  Each  Purchaser  acknowledges  that the Company
intends to pay a fee to SBC Warburg  Dillon Read Inc. and  Evolution  Capital in
respect of the sale of the Shares to the  Purchaser.  Each of the parties hereto
hereby  represents that, on the basis of any actions and agreements by it, there
are no other brokers or finders  entitled to compensation in connection with the
sale of the Shares to the Purchasers.

     9.3 Governing Law. This Agreement  shall be governed in all respects by and
construed  in  accordance  with the laws of the  State of New York  without  any
regard to conflicts of laws principles.

     9.4 Survival.  The  representations,  warranties,  covenants and agreements
made in this Agreement  shall survive any  investigation  made by the Company or
the Purchasers and the Closing.

     9.5  Successors  and  Assigns.  The  provisions  hereof  shall inure to the
benefit of, and be binding upon, the successors,  assigns,  heirs, executors and
administrators of the parties to this Agreement.  Notwithstanding the foregoing,
no Purchaser  shall assign this Agreement  without the prior written  consent of
the Company.

     9.6  Entire  Agreement.  This  Agreement  constitutes  the full and  entire
understanding  and  agreement  between the parties  with regard to the  subjects
thereof.

     9.7  Notices,  etc.  All  notices  and  other  communications  required  or
permitted  under this Agreement  shall be effective upon receipt and shall be in
writing and may be delivered in person, by telecopy,  overnight delivery service
or  registered or certified  United States mail  addressed to the Company or the
Purchasers,  as the case may be, at their respective  addresses set forth at the
beginning  of this  Agreement  or on Exhibit A or at such  other  address as the
Company or the  Purchasers  shall have  furnished to the other party in writing.
All  notices and other  communications  shall be  effective  upon the earlier of
actual  receipt  thereof by the person to whom  notice is directed or (i) in the
case of notices and  communications  sent by personal delivery or telecopy,  one
business  day after  such  notice or  communication  arrives  at the  applicable
address or was successfully sent to the applicable  telecopy number, (ii) in the
case of notices and communications  sent by overnight delivery service,  at noon
(local  time) on the  second  business  day  following  the day such  notice  or
communication was sent, and (iii) in the case of notices and communications sent
by United States mail seven days after such notice or  communication  shall have
been deposited in the United States mail.

     9.8  Severability  of this  Agreement.  If any provision of this  Agreement
shall be judicially  determined  to be invalid,  illegal or  unenforceable,  the
validity,  legality and enforceability of the remaining  provisions shall not in
any way be affected or impaired thereby.




                                      E-17
<PAGE>



     9.9  Counterparts.  This  Agreement  may  be  executed  in  any  number  of
counterparts,  each of which  shall be an  original,  but all of which  together
shall constitute one instrument.

     9.10 Further Assurances.  Each party to this Agreement shall do and perform
or cause to be done and  performed  all such  further  acts and things and shall
execute and deliver all such other  agreements,  certificates,  instruments  and
documents as the other party hereto may reasonably request in order to carry out
the intent and accomplish the purposes of this Agreement and the consummation of
the transactions contemplated hereby.

     9.11 Termination.  In the event that the Closing shall not have occurred on
or before sixty (60) days from the date hereof,  the  Purchasers  shall have the
option to terminate this Agreement at the close of business on such date, and in
the event that the Closing shall not have occurred on or before ninety (90) days
from the date hereof, this Agreement shall terminate at the close of business on
such date.

     9.12  Expenses.  The  Company  and each such  Purchaser  shall bear its own
expenses  incurred  on its  behalf  with  respect  to  this  Agreement  and  the
transactions contemplated hereby, including fees of legal counsel.

     9.13 Currency.  All references to "dollars" or "$" in this Agreement  shall
be deemed to refer to United States dollars.



                                      E-18
<PAGE>



     The  foregoing  agreement  is hereby  executed  as of the date first  above
written.


                                   "COMPANY"

                                   ENZON, INC.
                                   a Delaware corporation


                                   By:
                                      ------------------------------------------

                                   Title:
                                         ---------------------------------------


                                   "PURCHASERS"


                                   THE DCF LIFE SCIENCES FUND, LTD.



                                   By:
                                      ------------------------------------------

                                   Name:
                                        ----------------------------------------

                                   Title:
                                         ---------------------------------------



                                   DCF PARTNERS, L.P.



                                   By:
                                      ------------------------------------------

                                   Name:
                                        ----------------------------------------

                                   Title:
                                         ---------------------------------------









                                      E-19
<PAGE>



                                   ARIES DOMESTIC FUND, L.P.



                                   By:   
                                      ------------------------------------------

                                   Name: 
                                        ----------------------------------------

                                   Title:
                                         ---------------------------------------



                                   THE ARIES TRUST



                                   By:   
                                      ------------------------------------------

                                   Name: 
                                         ---------------------------------------

                                   Title:
                                         ---------------------------------------



                                   HAUSMANN HOLDINGS, N.V.



                                   By:   
                                      ------------------------------------------

                                   Name: 
                                         ---------------------------------------

                                   Title:
                                         ---------------------------------------














                                      E-20
<PAGE>



                                   ORACLE OFFSHORE LTD.



                                   By:   
                                      ------------------------------------------

                                   Name: 
                                        ----------------------------------------

                                   Title:
                                         ---------------------------------------



                                   ORACLE PARTNERS L.P.



                                   By:    
                                      ------------------------------------------

                                   Name:  
                                        ----------------------------------------

                                   Title: 
                                         ---------------------------------------



                                   ORACLE INSTITUTIONAL PARTNERS



                                   By:   
                                      ------------------------------------------

                                   Name: 
                                        ----------------------------------------

                                   Title:
                                         ---------------------------------------














                                      E-21
<PAGE>



                                   GSAM ORACLE FUND, INC.



                                   By:   
                                      ------------------------------------------

                                   Name: 
                                        ----------------------------------------

                                   Title:
                                         ---------------------------------------



                                   SBC WARBURG DILLON READ, INC.



                                   By:   
                                      ------------------------------------------

                                   Name: 
                                        ----------------------------------------

                                   Title:
                                         ---------------------------------------



                                   SBC WARBURG DILLON READ, INC.



                                   By:   
                                      ------------------------------------------

                                   Name: 
                                        ----------------------------------------

                                   Title:
                                         ---------------------------------------














                                      E-22
<PAGE>



                                   CACLUCEUS CAPITAL L.P.



                                   By:   
                                      ------------------------------------------

                                   Name: 
                                        ----------------------------------------

                                   Title:
                                         ---------------------------------------



                                   CACLUCEUS CAPITAL LTD.



                                   By:   
                                      ------------------------------------------

                                   Name: 
                                        ----------------------------------------

                                   Title:
                                         ---------------------------------------



                                   MERLIN BIOMED L.P.



                                   By:   
                                      ------------------------------------------

                                   Name: 
                                        ----------------------------------------

                                   Title:
                                         ---------------------------------------













                                      E-23
<PAGE>



                                   DEUTSCHE VERMOGEN SBILDUNGSGESELL
                                   SCHAFT MBH



                                   By:   
                                      ------------------------------------------

                                   Name: 
                                        ----------------------------------------

                                   Title:
                                         ---------------------------------------



                                   WAYNE P. ROTHBAUM



                                   By:   
                                      ------------------------------------------

                                   Name: 
                                        ----------------------------------------

                                   Title:
                                         ---------------------------------------



                                   MITCHELL D. SILBER



                                   By:   
                                      ------------------------------------------

                                   Name: 
                                        ----------------------------------------

                                   Title:
                                         ---------------------------------------













                                      E-24
<PAGE>



                                   NEW TECHNOLOGIES FUND




                                   By:
                                      ------------------------------------------

                                   Name:
                                        ----------------------------------------

                                   Title:
                                         ---------------------------------------







                                      E-25
<PAGE>

                                    Exhibit A
                                     to CSPA


<TABLE>
<CAPTION>
               Purchaser                           Shares       Purchase Price
               ---------                           ------       --------------
                                                             
<S>                                              <C>            <C>       
DCF Life Sciences Fund Ltd.                       200,000       $   950,000

DCF Partners, L.P.                                853,000       $ 4,051,750

     C/O DCF Capital
     660 Steamboat Road
     Greenwich, CT 06830
     Attn: Mr. Doug Floren
     Facsimile: (203) 618-1495

Oracle Partners, L.P.                             315,789       $ 1,499,997.75

Oracle Institutional Partners, L.P.                78,496       $   372,856

GSAM Oracle Fund, Inc.                            168,721       $   801,424.75

Haussmann Holdings, N.V                            50,526       $   239,998.50

Oracle Offshore Ltd.                               18,046       $    85,718.50

     C/O Oracle Partners, L.P.
     712 Fifth Avenue, 45th Floor
     New York, NY 10019
     Attn: Mr. Norman Schleffer
     Facsimile: (212) 459-0863

SBC Warburg Dillon Read, Inc.                     500,000       $ 2,375,000

     141 West Jackson Blvd.
     Chicago, IL  60604
     Attn: Mr. James Del Medico
     Facsimile: (312) 554-6332

Caduceus Capital L.P.                             105,000       $   498,750

Caduceus Capital Ltd.                             220,000       $ 1,045,000

     C/O Orbimed Advisors LLC
     767 Third Avenue, 6th Floor
     New York, NY 10017
     Attn: Mr. Sven H. Borho
     Facsimile: (212) 739-6444

Merlin BioMed LP                                   21,053       $   100,001.75

Deutsche Vermogen                                 294,737       $ 1,400,000.75
Sbildungsgesell Shaft mbH

     C/O Merlin Biomed
     237 Park Avenue, Suite 801
     New York, NY 10017
     Attn: Ms. Jennifer Stoler
     Facsimile: (212) 808-7422

The Aries Trust                                   747,368         3,549,998

Aries Domestic Fund, L.P.                         305,264         1,450,004

     C/O Paramount Capital Asset
       Management, Inc.
     787 Seventh Avenue
     New York, NY 10019
     Attn: Mr. David Tanen
     Facsimile: (212) 554-4355

Wayne P. Rothbaum                                  30,000       $   142,500

Mitchell D. Silber                                 15,000       $    71,250

     C/O The Carson Group
     156 West 56th Street
     10th Floor
     New York, NY 10019
     Attn: Mr. Wayne Rothbaum

New Technologies Fund                              60,000       $   285,000

     C/O Emerging Growth
       Management Co.
     One Embarcadero Center
     Suite 2410
     San Francisco, CA 94111
     Attn: Mr. Marc Pentopoulos
     Facsimile: (415) 782-9645
                                               ----------       --------------
                                                3,983,000       $18,919,250
                                               ==========       ==============
</TABLE>                                                   



                                      E-26
<PAGE>

                                    Exhibit B

                         INSTRUCTION SHEET FOR PURCHASER

                   (to be read in conjunction with the entire
                        Common Stock Purchase Agreement)

A.   Complete the following items in the Common Stock Purchase Agreement:

     1.   Provide the  information  regarding  the  Purchaser  requested  on the
          signature  page.  The  Agreement  must be  executed  by an  individual
          authorized to bind the Purchaser.

     2.   Exhibit B-1 - Stock Certificate Questionnaire:

          Provide   the   information   requested   by  the  Stock   Certificate
          Questionnaire;

     3.   Exhibit B-2 - Registration Statement Questionnaire:

          Provide  the  information  requested  by  the  Registration  Statement
          Questionnaire.

     4.   Exhibit B-3 - Purchaser Certificate:

          Provide the  information  requested by the  Certificate for Individual
          Purchasers  or the  Certificate  for  Corporate,  Partnership,  Trust,
          Foundation and Joint Purchasers, as applicable.

     5.   Return the signed Purchase Agreement  including the properly completed
          Exhibit 4.2 to:

                         Brobeck, Phleger & Harrison LLP
                         1633 Broadway, 47th Floor
                         New York, New York 10019
                         Telephone: (212) 581-1600
                         Attn: Heather Willens, Esq.

B.   Instructions  regarding  the  transfer of funds for the  purchase of Shares
     will be telecopied to the Purchaser by the Placement Agent at a later date.

C.   Upon the  resale of the  Shares  by the  Purchaser  after the  Registration
     Statement  covering the Shares is  effective,  as described in the Purchase
     Agreement, the Purchaser:

          (i)  must  deliver a current  prospectus,  and  annual  and  quarterly
               reports of the Company to the buyer (prospectuses, and annual and
               quarterly  reports  may  be  obtained  from  the  Company  at the
               Purchaser's request); and

          (ii) must send a letter in the form of  Exhibit  D to the  Company  so
               that the Shares may be properly transferred.



                                      E-27
<PAGE>

                                   Exhibit B-1

                                   ENZON, INC.

                         STOCK CERTIFICATE QUESTIONNAIRE


                  Pursuant to Section 4.3 of the  Agreement,  please  provide us
with the following information:


1.   The exact name that the Shares are to be
     registered in (this is the name that will
     appear on the stock certificate(s)). You may
     use a nominee name if appropriate:            _____________________________

2.   The relationship between the Purchaser of the
     Shares and the Registered Holder listed in
     response to item 1 above:                     _____________________________

3.   The mailing address of the Registered Holder
     listed in response to item 1 above:           _____________________________


                                                   _____________________________


                                                   _____________________________


                                                   _____________________________


                                                   _____________________________

4.   The Tax Identification Number of the
     Registered Holder listed in response to item
     1 above:                                      _____________________________







                                      E-28
<PAGE>



                                   Exhibit B-2

                                   ENZON, INC.

                      REGISTRATION STATEMENT QUESTIONNAIRE


     In connection with the preparation of the  Registration  Statement,  please
provide us with the following information regarding the Purchaser.

     1. Please state your organization's name exactly as it should appear in the
Registration Statement:


     2. Have you or your organization had any position, office or other material
relationship  within the past three  years  with the  Company or its  affiliates
other  than  as  disclosed  in  the  prospectus  included  in  the  Registration
Statement?

     _____ Yes        _____ No

     If yes, please indicate the nature of any such relationship below:


- --------------------------------------------------------------------------------


- --------------------------------------------------------------------------------


- --------------------------------------------------------------------------------


- --------------------------------------------------------------------------------




                                      E-29
<PAGE>



                                   Exhibit B-3

                                   ENZON, INC.

                      CERTIFICATE FOR INDIVIDUAL PURCHASERS


     If  the  investor  is an  individual  Purchaser  (or  married  couple)  the
Purchaser must complete, date and sign this Certificate.

                                   CERTIFICATE

     I  certify  that  the  representations  and  responses  below  are true and
accurate:

     In order for the Company to offer and sell the Shares in  conformance  with
state and federal  securities  laws, the following  information must be obtained
regarding your investor status.  Please initial each category  applicable to you
as an investor in the Company.

     ___ (1) A natural  person whose  individual  net worth,  or joint net worth
with that person's spouse, at the time of his purchase exceeds $1,000,000;

     ___ (2) A natural person who had an individual income in excess of $200,000
in each of the two most recent years,  or joint income with that person's spouse
in excess of $300,000, in each of those years, and has a reasonable  expectation
of reaching the same income level in the current year;

     ___ (3) An executive officer or director of the Company.




Dated: __________________           ____________________________________________
                                    Name(s) of Purchaser

                                    ____________________________________________
                                    Signature

                                    ____________________________________________
                                    Signature





                                      E-30
<PAGE>



                                   Exhibit B-4

                                   ENZON, INC.

                     CERTIFICATE FOR CORPORATE, PARTNERSHIP,
                     TRUST, FOUNDATION AND JOINT PURCHASERS


     If  the  investor  is a  corporation,  partnership,  trust,  pension  plan,
foundation,  joint purchaser  (other than a married couple) or other entity,  an
authorized  officer,  partner,  or  trustee  must  complete,  date and sign this
Certificate.

                                   CERTIFICATE

     The undersigned  certifies that the representations and responses below are
true and accurate:

     (a) The investor has been duly formed and is validly  existing and has full
power and  authority to invest in the Company.  The person  signing on behalf of
the  undersigned  has the  authority  to execute and  deliver  the Common  Stock
Purchase  Agreement on behalf of the  Purchaser  and to take other  actions with
respect thereto.

     (b) Indicate the form of entity of the undersigned:

         ____  Limited Partnership

         ____  General Partnership

         ____  Corporation

         ____  Revocable  Trust  (identify  each grantor and indicate under what
               circumstances the trust is revocable by the grantor):
               _________________________________________________________________
               _________________________________________________________________
               _________________________________________________________________
               _________________________________________________________________
               _________________________________________________________________
               ________.  (Continue on a separate piece of paper, if necessary.)

          ____ Other type of Trust (indicate type of trust and, for trusts other
               than pension trusts, name the grantors and beneficiaries):_______
               _________________________________________________________________
               _________________________________________________________________
               _________________________________________________________________
               ________.  (Continue on a separate piece of paper, if necessary.)



                                      E-31
<PAGE>

          ____ Other form of organization (indicate form of organization (____
               _______________________________________________________________).

     (c) Indicate the approximate date the undersigned entity was formed: ______
____________________.

     (d) In order for the  Company to offer and sell the  Shares in  conformance
with state and  federal  securities  laws,  the  following  information  must be
obtained regarding your investor status. Please initial each category applicable
to you as an investor in the Company.

          ____ 1. A bank as defined in Section 3(a)(2) of the Securities Act, or
               any savings and loan association or other  institution as defined
               in Section 3(a)(5)(A) of the Securities Act whether acting in its
               individual or fiduciary capacity;

          ____ 2. A broker or dealer  registered  pursuant  to Section 15 of the
               Securities Exchange Act of 1934;

          ____ 3. An  insurance  company  as  defined  in  Section  2(13) of the
               Securities Act;

          ____ 4. An investment  company registered under the Investment Company
               Act of 1940 or a  business  development  company  as  defined  in
               Section 2(a)(48) of that Act;

          ____ 5. A Small Business Investment Company licensed by the U.S. Small
               Business  Administration under Section 301(c) or (d) of the Small
               Business Investment Act of 1958;

          ____ 6. A plan  established  and maintained by a state,  its political
               subdivisions,  or any agency or instrumentality of a state or its
               political subdivisions, for the benefit of its employees, if such
               plan has total assets in excess of $5,000,000;

          ____ 7. An employee  benefit  plan within the meaning of the  Employee
               Retirement  Income  Security  Act  of  1974,  if  the  investment
               decision is made by a plan fiduciary, as defined in Section 3(21)
               of  such  Act,   which  is  either  a  bank,   savings  and  loan
               association, insurance company, or registered investment advisor,
               or if the  employee  benefit  plan has total  assets in excess of
               $5,000,000 or, if a self-directed plan, with investment decisions
               made solely by persons that are accredited investors;

          ____ 8. A private business  development  company as defined in Section
               202(a)(22) of the Investment Advisers Act of 1940;



                                      E-32
<PAGE>




          ____ 9. An organization described in Section 501(c)(3) of the Internal
               Revenue  Code,  corporation,  Massachusetts  or similar  business
               trust,  or  partnership,  not formed for the specific  purpose of
               acquiring the Shares, with total assets in excess of $5,000,000;

          ____ 10. A trust,  with  total  assets in excess  of  $5,000,000,  not
               formed for the specific  purpose of acquiring  the Shares,  whose
               purchase is directed by a  sophisticated  person as  described in
               Rule 506(b)(2)(ii) of the Exchange Act;

          ____ 11. An entity in which all of the equity owners qualify under any
               of the above  subparagraphs.  If the undersigned  belongs to this
               investor   category   only,   list  the  equity   owners  of  the
               undersigned,  and the  investor  category  which each such equity
               owner satisfies:

               _________________________________________________________________
               _________________________________________________________________
               _________________________________________________________________
               ________________________________________________________________.
               (Continue on a separate piece of paper, if necessary.)



Dated: _________________________, 19__

______________________________________
Name of investor



_____________________________________________________________
Signature and title of authorized officer, partner or trustee






                                      E-33
<PAGE>

                                    Exhibit C

                           Opinion of Company Counsel


                                      E-34
<PAGE>

                                    EXHIBIT C

                                                                           DRAFT



                              [Closing Date], 1998

[                 ]


     Re: Enzon, Inc. - Sale of Common Stock


Ladies and Gentlemen:

     We have acted as counsel to Enzon,  Inc. (the "Company") in connection with
the sale by the Company of shares of common stock of the Company (the  "Shares")
pursuant to the Common Stock  Purchase  Agreement  (the  "Purchase  Agreement"),
dated as of June [ ], 1998, by and between the Company and the investors  listed
on  Schedule A thereto  (the  "Purchasers").  This  opinion  is being  delivered
pursuant to Section 5.4 of the Purchase  Agreement.  All capitalized  terms used
herein and not defined  herein have the  meanings  assigned to such terms in the
Purchase Agreement.

     We have examined such  documents and have reviewed such questions of law as
we have  considered  necessary and  appropriate for the purposes of our opinions
set forth below.

     In rendering our opinions set forth below, we have assumed the authenticity
of all documents submitted to us as originals, the genuineness of all signatures
and the  conformity to authentic  originals of all documents  submitted to us as
copies. We have also assumed the legal capacity for all purposes relevant hereto
of all  natural  persons  and,  with  respect to all  parties to  agreements  or
instruments  relevant  hereto other than the Company,  that such parties had the
requisite power and authority  (corporate or otherwise) to execute,  deliver and
perform such agreements or instruments, that such agreements or instruments have
been duly  authorized  by all requisite  action  (corporate or otherwise) on the
part of such parties and have been duly  executed and  delivered by such parties
and that such agreements or instruments  are the valid,  binding and enforceable
obligations  of such parties.  As to questions of fact material to our opinions,
we have relied upon the representations  made in the Purchase Agreement and upon
certificates  of officers of the  Company  and of public  officials  (including,
without limitation, those certificates delivered to others at the Closing).




                                      E-35
<PAGE>



     Our opinions expressed below as to certain factual matters are qualified as
being  limited  "to our  knowledge"  or by other  words  to the same or  similar
effect.  Such words, as used herein, mean the information known to the attorneys
in the firm who have principally  represented the Company in connection with the
transactions contemplated by the Purchase Agreement. In rendering such opinions,
we have not  conducted any  independent  investigation  or consulted  with other
attorneys in our firm with respect to the matters covered thereby.  No inference
as to our knowledge  with respect to such matters  should be drawn from the fact
of our representation of the Company.

     Based on the foregoing, we are of the opinion that:

     1. The Company is a corporation duly incorporated,  validly existing and in
good standing under the laws of the State of Delaware.

     2. The  Company has the  corporate  power and  authority  to enter into the
Purchase  Agreement and to issue,  sell and deliver to the Purchasers the Shares
to be issued and sold by it thereunder.

     3.  The  Purchase  Agreement  has been  duly  authorized  by all  necessary
corporate  action  on the part of the  Company  and has been duly  executed  and
delivered by the Company.

     4.  The  performance  by the  Company  of the  Purchase  Agreement  and the
consummation by the Company of the transactions  therein  contemplated  will not
(a) violate any provision of the Company's  charter or bylaws or any  applicable
statute,  rule or regulation,  or (b) result in the material breach or violation
of  any of the  terms  and  provisions,  or  constitute  a  default  under,  any
indenture,  mortgage,  deed of trust,  loan  agreement,  bond,  debenture,  note
agreement or other  evidence of  indebtedness,  or any lease,  contract or other
agreement or instrument  known to us to which the Company is a party or by which
its properties are bound, or, to our knowledge, any order, writ or decree of any
court or governmental  agency or body having  jurisdiction over the Company,  or
over any of its properties or operations;  provided, however, that we express no
opinion herein regarding state or foreign securities or Blue Sky laws.

     5. The Purchase Agreement constitutes a valid and binding obligation of the
Company, enforceable against the Company according to its terms.




                                      E-36
<PAGE>



     6. The  Shares  to be issued by the  Company  pursuant  to the terms of the
Purchase  Agreement will be, upon issuance and delivery against payment therefor
in accordance  with the terms  thereof,  duly  authorized and validly issued and
fully  paid and  nonassessable,  and the  stockholders  of the  Company  have no
preemptive or other rights to purchase any of the Shares.

     The  opinions set forth above are subject to the  following  qualifications
and exceptions:

          (a)  Our  opinions  are  subject  to  the  effect  of  any  applicable
     bankruptcy, insolvency, reorganization,  moratorium or other similar law of
     general  application  affecting  creditors' or secured  creditors'  rights,
     including (without limitation) applicable fraudulent transfer laws.

          (b) Our  opinions are subject to the effect of general  principles  of
     equity,   including   (without   limitation)   concepts   of   materiality,
     reasonableness,  good faith and fair dealing,  and other similar  doctrines
     affecting the enforceability of agreements generally (regardless of whether
     considered in a proceeding in equity or at law).

          (c) Our opinions are subject to possible judicial action giving effect
     to governmental actions or foreign laws affecting creditors' rights.

          (d)  Our   opinions,   insofar  as  they  relate  to   indemnification
     provisions,  are subject to the effect of federal and state securities laws
     and public policy relating thereto.

     Our  opinions  expressed  above are  limited to the law of the State of New
York, the Delaware  General  Corporation Law, and the federal laws of the United
States of America.

     The foregoing  opinions are being  furnished to you solely for your benefit
and may not be relied upon by, nor may copies be delivered  to, any other person
without our prior written consent.

                                           Very truly yours,





                                      E-37
<PAGE>



                                    Exhibit D

                           OPINIONS OF PATENT COUNSEL






                                      E-38
<PAGE>

                   [LETTERHEAD OF ROBERTS & MERCANTI, L.L.P.]



                                 June 25, 1998

The Purchasers in the
Enzon, Inc. Common Stock
Purchase Agreement
dated June 25, 1998
and
SBC Warburg Dillon Read, Inc
535 Madison Avenue
New York, New York 10022

                 Re: Opinion of Intellectual Property Counsel with Respect to
                 Enzon's PEG INTRON A Technologies and Proprietary Rights 
                 Our Reference 213 1092
    
Ladies and Gentlemen:

     Our client, Enzon, Inc., a Delaware corporation (the "Company"), has
requested that we furnish to you our opinion in respect of certain matters
relating to the Company's PEG INTRON A technologies, and pursuant to Section 5.5
of the Common Stock Purchase Agreement, dated June 25, 1998, between SBC
Warburg Dillon Read, Inc. (the "Placement Agent") and the Company (the Placement
Agent Agreement"). Capitalized terms not otherwise defined herein shall have the
meaning ascribed to them, in the Purchase Agreement.

     For the purposes of rendering the opinions set forth below, we have either
reviewed the following in the course of preparing this opinion or else we have
reviewed the following in the course of our representation of the Company
(collectively the "Documents"):

     1.   the Purchase Agreement;

     2.   that certain Private Placement Offering Memorandum (the "Memorandum")
          dated June 2, 1998, together with any and all exhibits and amendments
          thereto;

     3.   the patents and patent applications listed on Schedule 1 attached
          hereto, which include all of the patents and patent applications
          referred to in the memorandum (the "Patents and Patent Applications")
          with respect to the Company's PEG


                                      E-39
<PAGE>


SBC Warburg Dillon Read, Inc.
June 25, 1998
Page 2


          INTRON A technologies and which are divided into category A, which are
          the patents and patent applications owned by the Company and the
          Company's subsidiaries listed on Schedule 2 attached hereto (the
          "Subsidiaries") (collectively, the "Owned Patent Rights")
          collectively, and category B, which are the patents and patent
          applications licensed by the Company and its Subsidiaries
          (collectively, the "Licensed Patent Rights");

     4.   copies of the license agreements listed on Schedule 3 attached hereto
          (collectively, the "License Agreements"); 

     5.   copies of assignments relevant to ownership of the Patents and Patent
          Applications, 

     6.   the results of searches in the United States Patent and Trademark
          Office ("USPTO"), completed on June 4, 1998 in relation to the USPTO's
          record of title to the United States patents and patent applications
          within the Patents and Patent Applications;

     7.   any and all references cited to, or by, the USPTO during the
          prosecution of the United States patents and patent applications
          included within the Patents and Patent Applications;

     8.   the documents referred to in those opinions of this firm which we
          delivered to the Company relating to the Owned Patent Rights or
          relating to whether the PEG INTRON A products or proposed products of
          the Company infringe patents belonging to any third parties;

     9.   the internal files of this firm pertaining to the Owned Patent Rights.

         Whenever our opinions herein are qualified by the phrase "to our best
knowledge," except as may be further qualified below, such language means
that based upon the Documents, the actual knowledge of attorneys within our firm
(i.e., not including matters as to which such attorneys could be deemed to have
constructive knowledge) and inquiries of officers, directors and employees of
the Company, we believe that such opinions are factually correct.

     (1)  To our best knowledge, the Company and its Subsidiaries are the sole
          owners of the Owned Patent Rights and have obtained currently
          effective licenses to the Licensed Patent Rights pursuant to the
          License Agreements.


                                      E-40
<PAGE>



SBC Warburg Dillon Read, Inc.
June 25, 1998
Page 3


     (2)  The Company and its Subsidiaries are listed in the records of the
          USPTO as the sole owners of the United States patents and patent
          applications within the Owned Patent Rights.

     (3)  The Licensors are listed in the records of the USPTO as the sole
          owners of the United States patents and patent applications within the
          Licensed Patent Rights.

     (4)  To our best knowledge, the Company and its Subsidiaries have good and
          marketable title to the Owned Patent Rights, free of any liens,
          pledges, claims, security interests or other encumbrances, but
          excluding those licenses set forth on Schedule 4.

     (5)  To our best knowledge, there is no information which would preclude
          the grant of patent from each of the patent applications within the
          Patents and Patent Applications, it being understood that there can be
          no certainty as to which adjustments may be made to the claims as part
          of the prosecution process within the PTO.

     (6)  To our best knowledge, the Company, the Subsidiaries and the Licensors
          have all complied with USPTO's duty of candor and disclosure for each
          of the United States patents and patent applications included in the
          Patents and Patent Applications.

     (7)  To our best knowledge, there is no information which forms a basis for
          a finding of unenforceability or invalidity of any of the claims of
          the Patents and Patent. Applications except for with regard to U.S.
          Patent No. 5,324,614; prior art uncovered after the '614 patent issued
          may be deemed to be such information either by itself or in
          combination with other information.

     (8)  There is no pending or, to our best knowledge, threatened action,
          suit, proceeding, or claim by others challenging the Company's or its
          Subsidiaries' ownership or license rights in or to any of the Owned
          Patent Rights or Licensed Patent Rights.


     (9)  There is no pending or, to our best knowledge, threatened action,
          suit, proceeding or claim by others challenging the validity or scope
          of any of the Owned Patent Rights or Licensed Patent Rights.

     (1O) There is no pending or, to our best knowledge, threatened action,
          suit, proceeding or claim by the Company or its Subsidiaries that a
          third party has or will infringe or otherwise violate any of the Owned
          Patent Rights or Licensed Patent Rights.


                                      E-41
<PAGE>


SBC Warburg Dillon Read, Inc.
June 25, 1998
Page 4


     (11) There is no pending or, to our best knowledge, threatened action,
          suit, proceeding or claim by any third party that the Company or its
          Subsidiaries or their products and processes infringe or otherwise
          violate any patent, trademark, copyright, trade secret or other right
          of such third party.

     (12) To our best knowledge, the statements in the Memorandum under the
          captions "Risk Factors - Patents and Proprietary Rights" and
          "Executive Summary" and other references in the Memorandum to the
          Intellectual Property and other patent, trade secret, trademark and
          licensing matters, insofar as such statements constitute a summary of
          the legal matters, documents or proceedings referred to therein, are
          accurate in all material respects and fairly present the information
          purported to be disclosed therein.

     We have participated in conferences with officials and other
representatives of the Company, Company's counsel and others, at which
conferences the contents of the Memorandum and related matters were discussed,
and although we have not verified the accuracy or completeness of the statements
contained in the Memorandum, nothing has come to our attention which leads us to
believe that the Memorandum or exhibits thereto (other than the financial
statements including supporting schedules and other financial and statistical
information derived therefrom) contained any untrue statement of a material fact
or omitted to state a material fact necessary to make the statements therein not
misleading.


                                           Sincerely,


                                           ROBERTS & MERCANTI, L.L.P.

                                           /s/MICHAEL N. MERCANTI
                                           ----------------------
                                           Michael N. Mercanti

MNM/aap


                                      E-42
<PAGE>


                                      DRAFT


                                           June 25, 1998



The Purchasers in the Enzon, Inc. 
     Common Stock
Purchase Agreement Dated June 25, 1998

and

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


Ladies and Gentlemen:

     Our client, Enzon, Inc., a Delaware corporation (the "Company"), has
requested that we furnish to you our opinion in respect of certain matters
relating to the Company's single chain antigen binding protein ("SCA")
technologies, and pursuant to Section 5.5 of the Common Stock Purchase
Agreement, dated June 25, 1998, between SBC Warburg Dillon Read, Inc. (the
"Placement Agent") and the Company (the "Placement Agent Agreement").
Capitalized terms not otherwise defined herein shall have the meaning ascribed
to them in the Purchase Agreement.

     For the purposes of rendering the opinions set forth below, we have either
reviewed the following in the course of preparing this opinion or else we have
reviewed the following in the course of our representation of the Company
(collectively the "Documents"):

     1.   the Purchase Agreement;


                                      E-43
<PAGE>


The Purchasers in the Enzon, Inc. Common Stock
and SBC Warburg Dillon Read, Inc.
June 25, 1998
Page 2


     2.   that certain Private Placement Offering Memorandum (the "Memorandum")
          dated June 2, 1998, together with any and all exhibits and amendments
          thereto;

     3.   the patents and certain patent applications listed on Schedule 1
          attached hereto, which include all of the patents and patent
          applications referred to in the Memorandum (the "Patents and Patent
          Applications") with respect to the Company's SCA technologies and
          which are divided into category A, which are the patents and patent
          applications owned by the Company and the Company's subsidiaries
          listed on Schedule 2 attached hereto (the "Subsidiaries")
          (collectively, the "Owned Patent Rights") collectively, and within
          category B, the issued U.S. patents licensed by the Company and its
          Subsidiaries no pending applications were examined in category B
          (collectively, the "Licensed Patent Rights");

     4.   copies of the license agreements listed on Schedule 3 attached hereto
          (collectively, the "License Agreements");

     5.   copies of assignments relevant to ownership of the Patents and Patent
          applications;

     6.   the results of searches in the United States Patent and Trademark
          Office ("USPTO"), completed on June 25, 1998 in relation to the
          USPTO's record of title to the United States patents and patent
          applications within the Patents and Patent Applications;

     7.   any and all references cited to, or by, the USPTO during the
          prosecution of the United States patents and patent applications
          included within Owned Patent Rights of the Patents and Patent
          Applications;

     8.   the documents referred to in those opinions of this firm which we
          delivered to the Company relating to the Owned Patent Rights or
          relating to whether the SCA products or proposed products of the
          Company infringe patents belonging to any third parties;

     9.   the internal files of this firm pertaining to the Owned Patent Rights.

     Whenever our opinions herein are qualified by the phrase "to our best
knowledge," except as may be further qualified below, such language means that
based upon the Documents, the


                                      E-44
<PAGE>


The Purchasers in the Enzon, Inc. Common Stock
and SBC Warburg Dillon Read, Inc.
June 25, 1998
Page 3


actual knowledge of attorneys within our firm (i.e., not including matters as to
which such attorneys could be deemed to have constructive knowledge) and
inquiries of officers, directors and employees of the Company, we believe that
such opinions are factually correct.

          (1) To our best knowledge, the Company and its Subsidiaries are the
     sole owners of the Owned Patent Rights and have obtained currently
     effective licenses to the Licensed Patent Rights pursuant to the License
     Agreements.

          (2) The Company and its Subsidiaries are listed in the records of the
     USPTO as the sole owners of the United Stated patents and patent
     applications within the Owned Patent Rights.

          (3) The Licensors are listed in the records of the USPTO as the sole
     owners of the United Stated patents within the Licensed Patent Rights. The
     undersigned can make no representation about the ownership of any pending
     patent applications of Licensors.

          (4) To our best knowledge, the Company and its Subsidiaries have good
     and marketable title to the Owned Patent Rights, free of any liens,
     pledges, claims, security interests or other encumbrances, but excluding
     those licenses set forth on Schedule 4.

          (5) To our best knowledge, there is no information which would
     preclude the grant of a patent from each of the patent applications within
     the Owned Patent Rights, it being understood that there can be no certainty
     as to which adjustments may be made to the claims as part of the
     prosecution process within the PTO. The undersigned can make no
     representation about the granting of any pending patent applications of
     third parties, such as Licensors.

          (6) To our best knowledge, the Company, and the Subsidiaries have all
     complied with USPTO's duty of candor and disclosure for each of the United
     Stated patents and patent applications included in the Owned Patent Rights.
     No representation can be made with respect to complying with the duty of
     candor by any Licensor.

          (7) To our best knowledge, there is no information which forms a basis
     for a finding of unenforceability or invalidity of any of the claims of the
     Owned Patent Rights.

          (8) There is no pending or, to our best knowledge, threatened action,
     suit, proceeding or claim by others challenging the Company's or its
     Subsidiaries' ownership or license rights in or to any of the Owned Patent
     Rights or Licensed Patent Rights.


                                      E-45
<PAGE>


The Purchasers in the Enzon, Inc. Common Stock
and SBC Warburg Dillon Read, Inc.
June 25, 1998
Page 4


          (9) There is no pending or, to our best knowledge, threatened action,
     suit, proceeding or claim by others challenging the validity or scope of
     any of the Owned Patent Rights.

          (10) There is no pending or, to our best knowledge, threatened action,
     suit, proceeding or claim by the Company or its Subsidiaries that a third
     party has or will infringe or otherwise violate any of the Owned Patent
     Rights or Licensed Patent Rights. However, the Company is constantly
     evaluating the activity of third parties and intends to enforce its patent
     rights when necessary and appropriate.

          (11) There is no pending or, to our best knowledge, threatened action,
     suit, proceeding or claim by any third party that the Company or its
     Subsidiaries or their products and processes infringe or otherwise violate
     any patent, trademark, copyright, trade secret, or other right of such
     third party.

          (12) To our best knowledge, the statements in the Memorandum under the
     captions "Risk Factors - Patents and Proprietary Rights" and "Executive
     Summary" and other references in the Memorandum to the Intellectual
     Property and other patent, trade secret, trademark and licensing matters,
     insofar as such statements constitute a summary of the legal matters,
     documents or proceedings referred to therein, are accurate in all material
     respects and fairly present the information purported to be disclosed
     therein.

     We have participated in conferences with officials and other
representatives of the Company, Company's counsel and others, at which
conferences the contents of the Memorandum and related matters were discussed,
and although we have not verified the accuracy or completeness of the statements
contained in the Memorandum, nothing has come to our attention which leads us to
believe that the Memorandum or exhibits thereto (other than the financial
statements including supporting schedules and other financial and statistical
information derived therefrom) contained any untrue statement of a material fact
or omitted to state a material fact necessary to make the statements therein not
misleading.

                                   Very truly yours,

                                   STERNE, KESSLER, GOLDSTEIN & FOX P.L.L.C.

                                   DRAFT

                                   Jorge A. Goldstein


JAG/aye



                                      E-46
<PAGE>


                                                                    Confidential


                       ENZON SCA(R) PROTEINS PATENT RIGHTS
                       -----------------------------------

<TABLE>
<CAPTION>
                                                  DATE                                                   DATE
TITLE             INVENTOR         COUNTRY        FILED          SERIAL NO.          PATENT NO.          ISSUED
- -----             --------         -------        -----          ----------          ----------          ------
<S>               <C>              <C>            <C>            <C>                 <C>                 <C>
Single            Ladner, Bird     US             09/02/86       06/902,971          Abandoned
Polypeptide                        US             09/02/87       07/902,110          Abandoned
Chain Molecules                    PCT            09/02/87       PCT/US87/02208
                                   EP             09/02/87       87906006.9          0281604             03/31/93
                                   Austria        09/02/87       87906006.9          0281604             03/31/93
                                   Belgium        09/02/87       87906006.9          0281604             03/31/93
                                   France         09/02/87       87906006.9          0281604             03/31/93
                                   Germany        09/02/87       87906006.9          0281604             03/31/93
                                   Italy          09/02/87       87906006.9          0281604             03/31/93
                                   Luxembourg     09/02/87       87906006.9          0281604             03/31/93
                                   Netherlands    09/02/87       87906006.9          0281604             03/31/93
                                   Sweden         09/02/87       87906006.9          0281604             03/31/93
                                   Switzerland    09/02/87       87906006.9          0281604             03/31/93
                                   U. Kingdom     09/02/87       87906006.9          0281604             03/31/93
                                   CA             09/04/87       546,164
                                   Japan          09/02/88       219589              Abandoned
                                   US             01/19/89       07/299,617          4,946,778           08/07/90
                                   US             04/25/90       07/512,910          5,260,203           11/09/93
                                   US             04/01/93       08/040,440          5,455,030           10/03/95
                                   US             06/06/95       08/468,988          5,518,889           05/21/96
                                   US             06/06/95       08/468,992          5,534,621           07/09/96

Computer Based    Ladner           US             09/02/86       06/902,970          4,704,692           11/03/87
System and                         PCT            09/02/87       PCT/US87/02211
Method for                         EP             09/02/87       87906007.7          Abandoned
Determining                        US             11/02/87       07/115,919          Abandoned
Possible                           US             06/09/88       07/204/940          4,881,175           Abandoned
Chemical
Structures

Organism          Ladner, Glick    US             03/02/87       07/021,046          Abandoned
Carrying a        Bird             PCT            03/02/88       PCT/US88/00716      
Single Chain                       EP             03/02/88       88903058.1          034978              11/30/94
Antibody                           France         03/02/88       88903058.1          034978              11/30/94
Domain                             Germany        03/02/88       88903058.1          034978              11/30/94
at its Surface                     U. Kingdom     03/02/88       88903058.1          034978              11/30/94
                                   US             07/30/89       07/373,702          Abandoned
                                   US             04/02/91       07/680,009          Abandoned
                                   US             11/04/91       07/802,631          Abandoned
                                   US             10/13/94       08/322,352          Abandoned

Incremental       Hardman          US             09/02/87       07/092,147          4,939,666           07/03/90
Macromolecule                      CA             09/01/88       576,286             Abandoned
Construction Method                JP             09/02/88       221223              Abandoned
</TABLE>


                                      E-47
<PAGE>


                                                                    Confidential


                       ENZON SCA(R) PROTEINS PATENT RIGHTS
                       -----------------------------------

<TABLE>
<CAPTION>
                                                  DATE                                                   DATE
TITLE             INVENTOR         COUNTRY        FILED          SERIAL NO.          PATENT NO.          ISSUED
- -----             --------         -------        -----          ----------          ----------          ------
<S>               <C>              <C>            <C>            <C>                 <C>                 <C>
                                   JP             11/20/92       510157              
Multivalent       Whitlow,         US             11/25/91       07/796,936          Abandoned
Antigen-          Wood             CA             11/20/92       2,122,732
Binding           Hardman          US             11/20/92       07/989,846          Abandoned
Proteins                           PCT            11/20/92       PCT/US92/09965
                                   EP             11/20/92       93900545.I
                                   US             02/22/95       08/392,338

Linkers for       Whitlow,         US             11/20/92       07/980,529          Abandoned
Linked fusion     Filpula          US             01/15/93       08/002,845          Abandoned
Polypeptides                       PCT            11/17/93       PCT/US93/11138      Abandoned
                                   US             04/07/94       08/224,591
                                   US             09/10/97       08/926,789

Antigen Binding   Whitlow,         US             10/13/94       08/232,445          5,763,733           06/09/98
Fusion Proteins   Filpula, Shorr   US             08/16/95       08/515,903
                                   PCT            10/13/95       PCT/US95/12840

Protein           Lee              US             04/07/95       08/417,855          5,656,730           08/12/97
Stabilized                         US             03/17/97       08/819,033
by Histidine

Production and    Filpula,         US             04/30/97       60/044,449          Abandoned
Uses of           Wang,            US             10/27/97       60/063,074
Glycosylated      Shorr,           US             12/02/97       60/067,341
Single Chain      Whitlow,         US             04/30/98       09/069,842
Fv Proteins       Lee              PCT            04/30/98

Polyalkylene      Shorr,           US             06/23/97       60/050,472
Glyco-Modified    Whitlow,         US             04/30/98       09/069,842
Single Chain      Filpula,         PCT            04/30/98       08654
Polypeptides      Lee
</TABLE>


June 2, 1998
u:\sca.con


                                      E-48
<PAGE>



                                   SCHEDULE 1B
                                   -----------


6/25/92              OIA Patent Applications/Issued Patents               Page 1

- --------------------------------------------------------------------------------
File No./                Docket No.          MSKCC Inventor(s)
Title of Disclosure      
- --------------------------------------------------------------------------------

SK 340                   25562               Lloyd et al

Monoclonal Antibodies to Human Gastrointestinal Cancer


Status of Disclosure: Abandoned for SK 340.1
- --------------------------------------------------------------------------------
Canada              Serial #: 507,097             Filing Date: 4/18/86
                    Patent #:                     Issue Date:
                    Status of Application:

- --------------------------------------------------------------------------------

PO         
         Serial #: 86104321.4          Filing Date: 3/27/86
                    Patent #:                     Issue Date:
                    Status of Application:

- --------------------------------------------------------------------------------

Japan               Serial #: 091154/86           Filing Date: 4/19/86
                    Patent #:                     Issue Date:
                    Status of Application:

- --------------------------------------------------------------------------------

U.S.                Serial #: 724,991             Filing Date: 4/19/85
                    Patent #:                     Issue Date:
                    Status of Application:        Abandoned for SK 340.1

- --------------------------------------------------------------------------------

SK 340.1                 25562-A             Lloyd et al

Monoclonal Antibodies to Human Gastrointestinal Cancer


Status of Disclosure: Abandoned for SK 340.2. Continuation of SK 340
- --------------------------------------------------------------------------------
U.S.                Serial #: 118,411             Filing Date: 11/06/87
                    Patent #:                     Issue Date:
                    Status of Application:        Abandoned for SK 340.2,
                                                  Continuation of SK 340
- --------------------------------------------------------------------------------


                                      E-49
<PAGE>


6/25/92              OIA Patent Applications/Issued Patents               Page 2

- --------------------------------------------------------------------------------
File No./                Docket No.          MSKCC Inventor(s)
Title of Disclosure      
- --------------------------------------------------------------------------------

SK 340.2                 25562-B             Welt et al

Method of Imaging Colorectal Carcinoma Lesion and Composition for use
therein


Status of Disclosure: Active.  CIP of SK 340.1
- --------------------------------------------------------------------------------
U.S.                Serial #: 327,765             Filing Date: 3/23/89
                    Patent #:                     Issue Date:
                    Status of Application:        Abandoned for SK 340.3
                                                  and SK 340.4, CIP of SK
- --------------------------------------------------------------------------------


SK 340.3                 25562-C             Welt et al

Method of Imaging Colorectal Carcinoma Lesion and Composition for use
therein


Status of Disclosure: Active.  Continuation of SK 340.2
- --------------------------------------------------------------------------------
U.S.                Serial #: 673,155             Filing Date: 3/18/91
                    Patent #:                     Issue Date:
                    Status of Application:        Divisional of SK 340.2
                                                  Abandoned
- --------------------------------------------------------------------------------


SK 340.4                 25562-D             Welt et al

Method of Imaging Colorectal Carcinoma Lesion and Composition for use
therein


Status of Disclosure: Active.  Divisional of SK 340.2
- --------------------------------------------------------------------------------
U.S.                Serial #: 671,132             Filing Date: 3/18/91
                    Patent #:                     Issue Date:
                    Status of Application:        Divisional of SK 340.2 
                                                  U.S. Patent 5,160,723   
- --------------------------------------------------------------------------------

U.S.                Serial #: 020,223             
                    Patent #: 5,431,897                    
                    Status of Application:        U.S. Patent 5,432,897   
- --------------------------------------------------------------------------------

U.S.                Serial #: 312,633             
                    Patent #: 5,643,550                    
                    Status of Application:        U.S. Patent 5,643,550   
- --------------------------------------------------------------------------------


                                      E-50
<PAGE>


                                  SCHEDULE 1B

                        PROTEIN ENGINEERING CORPORATION
                        -------------------------------

Title                    Inventor                Patent No.      Date Issued
- -----                    --------                ----------      -----------

Directed Evolution       Ladner, et. al.         5,223,409       06/29/93




                            AGEN BIOMEDICAL LIMITED
                            -----------------------

Title                    Country                 Serial No.
- -----                    -------                 ----------

Immunological Use        AU                      S0949/90
of Microwaves                                    (640634)
                         Int'l                   PCT/AU90/00040
                         CA                      2,046,621
                         EU                      90902980.3
                         US                      07/792,578



                            MOLECULAR ONCOLOGY, INC.

        U.S. Patent application Ser. No. 06/836,414; filed March 5, 1986



                                      E-51
<PAGE>


                                  SCHEDULE 1B

                               XOMA PATENT RIGHTS
<TABLE>
<CAPTION>
                                                             DATE
TITLE                   INVENTOR         COUNTRY             FILED          SERIAL NO.           PATENT NO.
- -----                   --------         -------             ------         ----------           ----------
<S>                     <C>              <C>                 <C>            <C>                  <C>           <C>
Modular Assembly        Robinson, Liu,   *United States      11/01/85       06/793,980     
of Antibody Genes,      Horwitz, Wall,   Australia           10/27/86       65981/86             606,320
Antibodies Prepared     Better           Austria             10/27/86       EP 86906676.1        0247091
Thereby and Use                          Belgium             10/27/86       EP 86906676.1        0247091
                                         Canada              10/31/86       521,909
                                         Denmark             10/27/86       3385/87
                                         Europe              10/27/86       EP 86906676.1        0247091
                                         Europe              10/27/86       92115754.1
                                         France              10/27/86       EP 86906676.1        0247091
                                         Germany             10/27/86       EP 86906676.1        0247091
                                         Italy               10/27/86       EP 86906676.1        0247091
                                         Japan               10/27/86       505887/86
                                         Luxembourg          10/27/86       EP 86906676.1        0247091
                                         Netherlands         10/27/86       EP 86906676.1        0247091
                                         PCT                 10/27/86       PCT/US88/02269
                                                                                                               (WO 87/02671)
                                         Sweden              10/27/86       EP 86906676.1        0247091
                                         Switzerland/
                                         Liechtenstein       10/27/86       EP 86906676.1        0247091
                                         Taiwan              11/27/86       75105650             51922
                                         United Kingdom      10/27/86       EP 86906676.1        0247091

Modular Assembly        Robinson, Liu,   Australia           07/25/88       23244/88             632462
of Antibody Genes,      Horwitz, Wall,   Austria             07/25/88       EP 88907510.7        0371998
Antibodies Prepared     Better           Belgium             07/25/88       EP 88907510.7        0371998
Thereby and Use                          Canada              07/24/88       572,398
                                         Denmark             07/25/88       0192/90
                                         Europe              07/25/88       EP 88907510.7        0371998
                                         Europe              07/25/88       EP 93100041.8

                                         France              07/25/88       EP 88907510.7        0371998
                                         Germany             07/25/88       EP 88907510.7        0371998
                                         Italy               07/25/88       EP 88907510.7        0371998
                                         Japan               07/24/88       506481/88
                                         Luxembourg          07/25/88       EP 88907510.7        0371998
                                         Netherlands         07/25/88       EP 88907510.7        0371998
                                         PCT                 07/25/88       PCT/US88/02514
                                                                                                               (WO 89/00999)
                                         Sweden              07/25/88       EP 88907510.7        0371998
                                         Switzerland/        
                                         Liechtenstein       07/25/88       EP 88907510.7        0371998
                                         United Kingdom      07/25/88       EP 88907510.7        0371998
                                         *United States      07/24/87       07/077,528
                                         United States       03/28/90       07/501,092
                                         United States       12/08/92       07/987,555
                                         United States       04/17/92       07/870,404
                                         United States       02/22/93       08/020,671
                                         United States       04/29/94       08/235,225
                                         United States       08/18/94       08/299,085
                                         United States       12/09/94       08/367,234

AraB Promoters          Lai, Lee, Lin    Austria             01/24/86       EP 86900983.7        0211047
and Method of           Ray, Wilcox      Belgium             01/24/86       EP 86900983.7        0211047
Producing                                Europe              01/24/86       EP 86900983.7        0211047
Polypeptides                             Finland             01/24/86       863891
Including                                France              01/24/86       EP 86900983.7        0211047
Cecropins by                             Germany             01/24/86       EP 86900983.7        0211047
Microbiological                          Italy               01/24/86       EP 86900983.7        0211047
Techniques                               Japan               01/24/86       500818/88
                                         Luxembourg          01/24/86       EP 86900983.7        0211047
                                         Netherlands         01/24/86       EP 86900983.7        0211047
                                         Norway              01/24/86       863808
                                         PCT                 01/24/86       PCT/US86/00131
</TABLE>


                                      E-52
<PAGE>



<TABLE>
<S>                     <C>              <C>                 <C>            <C>                  <C>           <C>
                                                                                                               (WO 86/04356)
                                         Sweden              01/24/86       EP 86900983.7        0211047
                                         Switzerland/        
                                         Liechtenstein       01/24/86       EP 86900983.7        0211047
                                         United Kingdom      01/24/86       EP 86900983.7        0211047
                                         *United States      01/28/85       06/695,309
                                         *United States      11/13/85       06/797,472
                                         United States       02/05/90       07/474,304           5,028,530

Novel Plasmid           Lei, Wilcox      Australia           01/09/89       29377/89             627443
Vector With                              Canada              01/10/89       587,885
Pectate Lyase                            Europe              01/09/89       EP 89901763.6
Signal Sequence                          Japan               01/09/89       501661/89
                                         PCT                 01/09/89       PCT/US89/00077                     (WO 89/06283)

                                         *United States      01/11/88       07/142,089
</TABLE>


                                      E-53
<PAGE>


                                   SCHEDULE 2
                                   ----------

                                  Subsidiaries
                                  ------------



                                Enzon Labs, Inc.

                                  Symvex, Inc.

                                   Enzon GmbH


                                      E-54
<PAGE>


                                   SCHEDULE 3
                                   ----------

                                IN-LICENSES - SCA
                                -----------------



                    Agen Biomedical Limited
                    Memorial Sloan Kettering
                    Protein Engineering Corporation
                    XOMA



                                      E-55
<PAGE>


                                   SCHEDULE 4
                                   ----------

                               OUT-LICENSES - SCA
                               ------------------



                    Alexion Pharmaceuticals, Inc.
                    Baxter Healthcare Corporation
                    Bristol-Myers Squibb Corporation
                    Cambridge Antibody Technology Limited
                    Creative BioMolecules
                    Cell Genesys, Inc.
                    Cytoclonal Pharmaceutics, Inc.
                    Hybritech Incorporated
                    Invitrogen, Inc.
                    Neoprobe Corporation
                    PanVera Corporation
                    Pharmacia Biotech, Inc.
                    Pharmacia P-L Biochemicals, Inc.
                    Rhone Poulenc Rorer (Gencell)
                    Molecular Oncology, Inc. (MOI)
                    XOMA
                

                                      E-56
<PAGE>

                                    Exhibit E

                     PURCHASER'S LEGEND REMOVAL CERTIFICATE

To:  [Transfer agent name and address]

     Attention: ______________

     The  undersigned,  the  Purchaser  or an officer  of, or other  person duly
authorized by the Purchaser, hereby certifies that _____________________________
                                                    (fill in name of Purchaser)
institution  was  the  Purchaser  of  the  Shares   evidenced  by  the  attached
certificate,  and in order to induce the Company to remove the legends contained
on the  certificates  representing the Common Stock purchased by such Purchaser,
Purchaser  will  sell  such  Shares  (i) in  accordance  with  the  registration
statement,  file number in which case the Purchaser will satisfy the requirement
of  delivering a current  prospectus  in  connection  with such sale, or (ii) in
accordance with Rule 144 under the Securities Act of 1933 ("Rule 144"), in which
case the Purchaser  certifies  that it has complied with or will comply with the
requirements of Rule 144. Print or type:

     Name of Purchaser:  _______________________________________________________

     Name of Individual
      representing
      Purchaser (if an
      Institution):      _______________________________________________________

     Title of Individual
      representing
      Purchaser (if an
      Institution):      _______________________________________________________

Signature by:

         Purchaser or
          Individual representing
          Purchaser:     _______________________________________________________




                                      E-57
<PAGE>




                                    Exhibit F

                   PURCHASER'S CERTIFICATE OF SUBSEQUENT SALE

To:  [Transfer agent name and address]

     Attention: _____________

     The  undersigned,  the  Purchaser  or an officer  of, or other  person duly
authorized by the Purchaser, hereby certifies that _____________________________
                                                    (fill in name of Purchaser)
institution  was  the  Purchaser  of  the  Shares   evidenced  by  the  attached
certificate,  and  as  such,  proposes  to  transfer  such  Shares  on  or about
______________________ either (i) in accordance with the registration statement,
       (date)
file  number  _____________,  in which  case the  Purchaser  certifies  that the
requirement of delivering a current prospectus has been complied with or will be
complied with in connection  with such sale, or (ii) in accordance with Rule 144
under the  Securities  Act of 1933  ("Rule  144"),  in which case the  Purchaser
certifies that it has complied with or will comply with the requirements of Rule
144.

Print or type:

         Name of Purchaser:  ___________________________________________________

         Name of Individual
          representing
          Purchaser (if an
          Institution):      ___________________________________________________

         Title of Individual
          representing
          Purchaser (if an
          Institution):      ___________________________________________________

Signature by:



                                      E-58
<PAGE>


                                    Exhibit G

                          DESCRIPTION OF CAPITAL STOCK




                                      E-59
<PAGE>

                                    EXHIBIT G

                          Description of Capital Stock

     Under its Certificate of Incorporation,  the Company is authorized to issue
60,000,000  shares of Common  Stock,  par value  $.01 per share,  and  3,000,000
shares of preferred  stock,  par value $.01 per share. As of May 29, 1998, there
were  31,331,081  shares of Common Stock,  and 108,000 shares of preferred stock
designated  as Series A Preferred  Stock,  outstanding.  Other than the Series A
Preferred Stock, there are no other classes of preferred stock designated and no
other shares of preferred stock  outstanding.  Holders of shares of Common Stock
and Series A Preferred Stock are entitled to one vote per share on matters to be
voted upon by the  stockholders of the Company.  There are no cumulative  voting
rights and, accordingly,  the holders of a majority of the combined Common Stock
and Series A Preferred  Stock may elect all of the  directors.  The Common Stock
and the Series A Preferred  Stock  shall be voted as one class,  except (i) with
respect to any action  amending or  repealing  any of the powers,  designations,
preferences  and rights of the Series A  Preferred  Stock,  which  requires  the
affirmative  vote of holders of not less than two-thirds of the then outstanding
Series A  Preferred  Stock and (ii) with  respect  to any action  increasing  or
decreasing  the  authorized  shares  or the par  value  of the  Common  Stock or
preferred stock or altering or changing  adversely the powers,  preferences,  or
special  rights of such  shares,  which  pursuant to Section 242 of the Delaware
General  Corporation  Law  requires  the  affirmative  vote of a majority of the
outstanding  shares  of the class so being  affected,  voting as a class and the
affirmative  vote of a majority of the  combination  of the  outstanding  Common
Stock and Series A Preferred Stock, voting as one class.

Common Stock

     Holders of shares of Common  Stock will be  entitled  to receive  dividends
when,  as and if declared by the Board of Directors  and to share ratably in the
assets of the Company legally  available for distribution to its stockholders in
the event of the liquidation,  dissolution or winding up of the Company, in each
case  subject to the rights of the  holders  of the  Series A  Preferred  Stock.
Holders  of  Common  Stock  have  no  preemptive,  subscription,  redemption  or
conversion  rights. All of the issued and outstanding shares of Common Stock are
duly authorized, validly issued, fully-paid and non-assessable.

     The registrar and transfer agent for the Common Stock is Continental  Stock
Transfer and Trust Company, 2 Broadway, New York, New York 10004.

     The authorized but unissued  preferred  stock may be issued by the Board of
Directors from time to time in one or more series with such  preferences,  terms
and rights as the Board of Directors may determine without further action by the
stockholders of the Company.  Accordingly,  the Board of Directors has the power
to fix the dividend rate and to establish the  provisions,  if any,  relating to
voting  rights,



                                      E-60
<PAGE>


redemption rates,  sinking fund,  liquidation  preferences and conversion rights
for any series of preferred stock issued in the future.

     It is not possible to state the actual effect of the  authorization  of the
preferred  stock upon the rights of holders of the Common  Stock until the Board
of Directors  determines  the specific  rights of the holders of a series of the
preferred  stock.  The  issuance of the  preferred  stock may have the effect of
delaying,  deferring or  preventing  a change in control of the Company  without
further action by the stockholders.

Series A Preferred Stock

     The  holders  of the Series A  Preferred  Stock are  entitled  to an annual
dividend of $2.00 per share, payable semi-annually but only when and if declared
by the Board of Directors out of funds legally available therefor.  Dividends on
the Series A  Preferred  Stock are  cumulative  and accrue  and  accumulate.  No
dividends are to be paid or set apart for payment on the Common  Stock,  nor are
any shares of Common  Stock to be redeemed,  retired or  otherwise  acquired for
valuable  consideration unless the Company has paid in full, or made appropriate
provision for the payment in full of, all dividends which have then  accumulated
on the Series A Preferred Stock.

     Since the Company did not make cash dividend payments for eight semi-annual
periods from the date of issuance of the Series A Preferred Stock, any holder of
Series A Preferred  Stock may elect,  upon written notice to the Company,  to be
paid all or any part of such  accrued and unpaid  dividends,  and any  dividends
which  accrue  but are not  paid in cash  within  thirty  days of the  scheduled
payment date thereafter,  in shares of the Company's  Common Stock.  Accrued and
unpaid  dividends  payable to holders of Series A Preferred Stock as of the date
such holder  elects to convert the Series A  Preferred  Stock into Common  Stock
may, at the Company's option, be paid by the Company's  issuance of Common Stock
to such holder. In all cases the number of shares of Common Stock to be received
in lieu of accrued  dividends  shall be  determined  by dividing  the  aggregate
amount of the accrued and unpaid  dividends by the conversion rate of the Series
A Preferred  Stock in effect on the date of election.  To date,  the Company has
paid no dividends on the Series A Preferred Stock,  except for accrued dividends
payable on Series A Preferred Stock which has been converted,  all of which have
been paid with Common Stock.  The Company does not presently  intend to pay cash
dividends on the Series A Preferred  Stock.  There were 1,733,000 of accrued and
unpaid dividends on the Series A Preferred Stock as of March 31, 1998. Dividends
on the Series A Preferred  Stock  currently  accrue at the rate of $216,000  per
year.

     Each share of Series A Preferred  Stock is convertible at any time prior to
redemption.  For purposes of conversion,  each share of Series A Preferred Stock
is deemed to have a value of $25.00. The Series A Preferred Stock is convertible
into  Common  Stock at a  conversion  rate of $11.00 per share of Common  Stock.
The 


                                      E-61
<PAGE>


conversion rate will be adjusted upon the Company's  payment of dividends on its
Common Stock in Common  Stock,  the  subdivision  or reduction of the  Company's
outstanding Common Stock, the reclassification of the Common Stock or the merger
or consolidation of the Company,  provided,  however, that no such adjustment to
the conversion  rate will be made unless the net effect on the conversion  price
per share of all such events is at least $.50 in the aggregate.

     The Company  may at any time,  redeem the whole or any part of the Series A
Preferred Stock then outstanding at a redemption price of $25.00 per share, plus
in each case a sum equal to all accumulated and unpaid dividends thereon through
the date fixed for redemption.  In case of redemption of only part of the Series
A Preferred  Stock at any time  outstanding,  the Company  shall  designate  the
amount of Series A  Preferred  Stock so to be  redeemed  and shall  redeem  such
Series A Preferred  Stock on a pro rata basis.  Subject to certain  limitations,
the Board of Directors shall have the power and authority to prescribe the terms
and  conditions  upon which the Series A Preferred  Stock shall be redeemed from
time to time.

     In the event of any voluntary or  involuntary  liquidation,  dissolution or
winding  up of the  Company,  the  holders of Series A  Preferred  Stock will be
entitled  to  receive  in cash out of the assets of the  Company,  whether  from
capital or from earnings, available for distribution to its stockholders, before
any amount shall be paid to the holders of the Common  Stock,  the sum of $25.00
per share of Series A Preferred  Stock,  plus an amount equal to all accumulated
and  unpaid  dividends  thereon  through  the date  fixed  for  payment  of such
distributive amount.

     All shares of Common  Stock are of junior rank to Series A Preferred  Stock
in respect of the preferences as to dividends,  distributions  and payments upon
the  liquidation,  dissolution  or winding up of the Company.  The rights of the
holders of the Common Stock are subject to the  preferences  and relative rights
of the Series A Preferred  Stock. The Company may authorize and issue additional
or other  Preferred  Stock  which is of equal rank with the  Series A  Preferred
Stock in respect of the preferences as to dividends,  distributions and payments
upon the  liquidation,  dissolution  or  winding  up of the  Company;  provided,
however,  that for so long as any Series A Preferred Stock remains  outstanding,
the Company  shall not issue any capital stock which is more senior in rank than
the Series A Preferred  Stock in respect of the foregoing  preferences  or which
shall have greater voting rights than the Series A Preferred Stock. In the event
of a merger or  consolidation  of the Company with or into another  corporation,
the Series A Preferred  Stock shall maintain its relative  powers,  designations
and preferences.

Common Stock Purchase Warrants

     As of May 29,  1998 the  Company  had  outstanding  warrants to purchase an
aggregate of 1,038,686  shares of Common Stock at exercise  prices  ranging from
$2.50 to $ 5.63 per share.


                                      E-62
<PAGE>


Options to Purchase Common Stock

     As of May 29,  1998 the  Company  had  outstanding  options to  purchase an
aggregate of 4,378,736  shares of Common Stock at exercise  prices  ranging from
$1.88 to $14.88 per share held by employees, directors and consultants under the
Company's Non-Qualified Stock Option Plan.

Independent Directors Stock Plan

     Under the terms of the Company's Independent Directors Stock Plan (approved
by stockholders in December 1996) each independent director is granted shares of
Common Stock equivalent to $2,500 per quarter, plus $500 for Board of Directors'
meeting attended.  The number of shares issued is based on the fair market value
of the Common Stock on the last trading day of the applicable quarter.

Registration Rights

     Schering  Corporation  has  piggyback  registration  rights with respect to
847,489  shares of Common Stock.  Such shares are eligible  under Rule 144(k) of
the Securities Act of 1933, as amended.



                                      E-63




                                                                     Exhibit 4.2

                             CERTIFICATE OF AMENDENT

                                       OF

                          CERTIFICATE OF INCORPORATION

                                       OF

                                   ENZON, INC.

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

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

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

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

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

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

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


                                      E-64
<PAGE>


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

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

ATTEST

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

                                      E-65




                                                                     EXHIBIT 5.1

                        [DORSEY & WHITNEY LLP LETTERHEAD]

                                  July 9, 1998

Enzon, Inc.
20 Kingsbridge Road

Piscataway, New Jersey 08854

     Re:  Registration Statement on Form S-3 (File No. 333-58269)
          -------------------------------------------------------

Ladies and Gentlemen:

          You have  requested  our opinion with respect to the  registration  by
     Enzon,  Inc. (the "Company")  pursuant to a Registration  Statement on Form
     S-3 (the  "Registration  Statement")  under the  Securities Act of 1933, as
     amended (the "Act"),  of an aggregate of 3,983,000 shares (the "Shares") of
     the Company's  Common Stock,  $.01 par value per share (the "Common Stock")
     which  may be sold  from  time to time by the  selling  stockholders  named
     therein (the "Selling Stockholders").  

          In so acting,  we have  examined  originals  or copies,  certified  or
     otherwise  identified to our  satisfaction,  of such  documents,  corporate
     records,  certificates of public  officials and other  instruments and have
     conducted  such  other  investigations  of fact  and law as we have  deemed
     relevant  and  necessary  to form a  basis  for  the  opinions  hereinafter
     expressed.  In conducting  such  examination,  we have assumed (i) that all
     signatures are genuine,  (ii) that all documents and instruments  submitted
     to us as copies conform with the originals, and (iii) the due execution and
     delivery  of  all  documents   where  due  execution  and  delivery  are  a
     prerequisite to the effectiveness thereof. As to any facts material to this
     opinion, we have relied upon statements and representations of officers and
     other  representatives  of the Company and certificates of public officials
     and have not independently verified such facts.

          Based  solely upon the  foregoing,  it is our opinion that the Shares,
     when  issued in  accordance  with the terms of the  Common  Stock  Purchase
     Agreement  dated as of June  25,  1998 by and  among  the  Company  and the
     Selling  Stockholders,  will  constitute  validly  issued,  fully  paid and
     non-assessable shares of Common Stock of the Company.

          Our  opinions  expressed  above are limited to the law of the State of
     New York, the Delaware General Corporation Law, and the federal laws of the
     United States of America.



                                      E-66
<PAGE>



          We hereby  consent to the filing of this  opinion as an exhibit to the
     Registration Statement,  and to the reference to our firm under the heading
     "Legal  Matters" in the Prospectus  constituting  part of the  Registration
     Statement relating to the registration of the Shares.

                                       Very truly yours,

                                       

                                       /S/ DORSEY & WHITNEY LLP
                                       ------------------------
                                        Dorsey & Whitney LLP





                                      E-67




                                                                    EXHIBIT 23.2

                          INDEPENDENT AUDITORS' CONSENT

The Board of Directors
Enzon, Inc.

We consent to the use of our reports incorporated herein by reference and to the
reference to our firm under the heading "Experts" in the Prospectus.


                                                 /s/ KPMG Peat Marwick LLP
                                                 -------------------------
                                                 KPMG Peat Marwick LLP

Short Hills, New Jersey
July 9, 1998

                                      E-68



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