i


                              DEVELOPMENT AGREEMENT

                                     BETWEEN

                           INEX PHARMACEUTICALS, INC.

                                       AND

                           ENZON PHARMACEUTICALS, INC.

                                January 19, 2004

<PAGE>

                              Development Agreement

                                Table of Contents

Article 1 Interpretation .................................................    3
   1.1   Definitions .....................................................    3
   1.2   Entire Agreement; Conflicts .....................................   12
   1.3   Governing Law ...................................................   12
   1.4   Headings ........................................................   12
   1.5   Severability ....................................................   13

Article 2 Grant and Reservation of Rights ................................   13
   2.1   Grant of Licenses 10
   2.2   Reservation of Rights ...........................................   13
   2.3   *** ....................................   Error! Bookmark not defined.
   2.4   Sublicenses .....................................................   14

Article 3 Milestone Payments for Development .............................   15
   3.1   Signing and Regulatory Milestone Payments .......................   15
   3.2   Withholding Taxes ...............................................   16
   3.3   Late Payments ...................................................   17

Article 4 Development ....................................................   17
   4.1   Development Activities in accordance with the Development Plan ..   17
   4.2   Overview of Development .........................................   18
   4.3   Development Diligence ...........................................   18
   4.4   Development Plans ...............................................   18
   4.5   Reports on Development ..........................................   19
   4.6   Attendance at Regulatory Meetings ...............................   19
   4.7   Subcontractors ..................................................   19

Article 5 Development Responsibility and Funding .........................   19
   5.1   Shared Funding of Certain Development Costs .....................   19
   5.2   Development Clinical Activities .................................   19
   5.3   Post-Approval Clinical Activities ...............................   20
   5.4   Regulatory Activities ...........................................   20
   5.5   Filing of Regulatory Submissions ................................   21
   5.6   Technical and Manufacturing Support Activities ..................   21
   5.7   Funding of Development Costs ....................................   21
   5.8   Transition ......................................................   22
   5.9   Records .........................................................   22
   5.10  Audits ..........................................................   22

Article 6 Joint Steering Committee .......................................   23
   6.1   Joint Steering Committee ........................................   23
   6.2   Meetings of the Joint Steering Committee ........................   24
   6.3   Working Committees ..............................................   24

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>

                                       iii


Article 7 Pharmacovigilance, DDMAC and Recalls ...........................   24
   7.1   Regulatory Responsibilities .....................................   24
   7.2   Pharmacovigilance Agent .........................................   25
   7.3   Agency for DDMAC Activities .....................................   26
   7.4   Agent for Regulatory Authorities Generally ......................   26
   7.5   Recalls and Withdrawals of Product ..............................   26

Article 8 Additional Opportunities .......................................   27
   8.1   Pipeline Drug ...................................................   27
   8.2   Legal Effect ....................................................   27

Article 9 Representations and Warranties .................................   27
   9.1   By Enzon ........................................................   27
   9.2   By Inex .........................................................   28
   9.3   Survival of Representations and Warranties ......................   30
   9.4   DISCLAIMER ......................................................   30

Article 10 Intellectual Property Rights ..................................   30
   10.1  Injunctive Relief ...............................................   30
   10.2  Ownership of Pre-Existing Intellectual Property Rights ..........   31
   10.3  Ownership of Intellectual Property Rights in the Product ........   31
   10.4  Ownership of Regulatory Approvals and Regulatory Submissions ....   31
   10.5  Ownership of Intellectual Property Rights Outside the Development   31

Article 11 Termination ...................................................   32
   11.1  Term ............................................................   32
   11.2  Renewal .........................................................   32
   11.3  Voluntary Termination ...........................................   32
   11.4  Termination for Breach ..........................................   33
   11.5  Termination upon Bankruptcy .....................................   33
   11.6  Survival of Obligations; Return of Confidential Information .....   34
   11.7  Additional Consequences of Termination ..........................   34
   11.8  Termination on a Country by Country Basis .......................   35
   11.9  Termination of Related Agreements ...............................   35

Article 12 Miscellaneous .................................................   36
   12.1  Assignment ......................................................   36
   12.2  Counterparts ....................................................   36
   12.3  Force Majeure ...................................................   36
   12.4  Further Assurances ..............................................   37
   12.5  International Sale of Goods Act .................................   37
   12.6  Modification ....................................................   37
   12.7  No Agency .......................................................   37
   12.8  No Solicitation or Hiring of Employees ..........................   37
   12.9  Non-Use of Names ................................................   37
   12.10 Notices .........................................................   37
   12.11 Publicity .......................................................   39
   12.12 No Third Party Beneficiaries ....................................   39
   12.13 Waiver ..........................................................   40
   12.14 Cross Default ...................................................   40

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       3

                              Development Agreement

This DEVELOPMENT AGREEMENT dated as of the 19th day of January, 2004 between
Inex Pharmaceuticals, Inc., a corporation duly incorporated pursuant to the laws
of Delaware, USA, having a registered office at Corporation Trust Center, 1209
Orange Street, Wilmington, DE 19801 (hereinafter referred to as "Inex"), and
Enzon Pharmaceuticals, Inc., a corporation duly incorporated pursuant to the
laws of Delaware, having a principal place of business at 685 Route 202/206,
Bridgewater, New Jersey 08807, USA (hereinafter referred to as "Enzon").

INTRODUCTION

A. Enzon is a pharmaceutical company with operations in research and
development, import, export, manufacture and sale of pharmaceutical products;

B. Inex is in the business of developing, manufacturing and selling certain
pharmaceutical products, including Vincristine Sulfate Liposomes Injection (as
further defined in this Agreement);

C. Of even date hereof, the Parties have entered into a Product Supply Agreement
for the supply from Inex to Enzon of Vincristine Sulfate Liposomes Injection,
and incidental thereto, the Parties must complete the development of Vincristine
Sulfate Liposomes Injection;

D. Inex and Enzon desire to set out in this Agreement the terms which will
govern the development of Vincristine Sulfate Liposomes Injection and to provide
for licenses for the right to develop, market and distribute Vincristine Sulfate
Liposomes Injection, which licenses are granted solely for the Parties' legal
protection and for the purpose of enabling Enzon to acquire rights to develop,
market, distribute and sell Inex's Vincristine Sulfate Liposomes Injection
product in the Territory for the Term;

E. The execution of this Agreement is ancillary to and a necessary pre-condition
for the establishment of both a market and a product for Inex's business with
respect to manufacturing and selling Vincristine Sulfate Liposomes Injection.

In consideration of the mutual covenants and promises contained in this
Agreement and other good and valuable consideration, and intending to be legally
bound, Inex and Enzon agree as follows:

                            Article 1 Interpretation

1.1   Definitions

Unless otherwise defined in this Agreement, capitalized terms used in this
Agreement shall have the meaning set out therefor in the Product Supply
Agreement. As used in this Agreement, the following terms, whether used in the
singular or plural, shall have the following meanings:

      1.1.1   "Adverse Drug Event" will have the meaning set forth in Exhibit
              1.1.1.

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       4


      1.1.2   "Affiliate" means any corporation, company, partnership, joint
              venture or other person or entity which controls, is controlled by
              or is under common control with a Party. For purposes of this
              Section 1.1.1, "control" shall mean (a) in the case of corporate
              entities, direct or indirect ownership of at least 50% of the
              stock or shares (or such lesser percentage which is the maximum
              allowed to be owned by a foreign corporation in a particular
              jurisdiction) entitled to vote for the election of directors or
              otherwise having the power to vote on or direct the affairs of
              such Party; and (b) in the case of non-corporate entities, direct
              or indirect ownership of at least 50% of the equity interest or
              the power to direct the management and policies of such
              non-corporate entities.

      1.1.3   "Agreement" means this Development Agreement including all
              exhibits attached to this Agreement.

      1.1.4   "Applicable Laws" means all applicable federal, provincial, state
              and local laws, ordinances, rules and regulations of any kind
              whatsoever in the Territory, including, without limitation,
              pharmaceutical and environmental rules and regulations, including
              cGMP Requirements, GCP Requirements, GLP Requirements and the
              General Biological Products Standards of the FDA, and the Federal
              Food, Drug and Cosmetic Act, as amended, or any successor act
              thereto ("FDCA").

      1.1.5   "Business Day" means any day other than a day which is a Saturday,
              a Sunday or a statutory holiday in New York City, New York, USA.

      1.1.6   "cGMP Requirements" shall mean the current Good Manufacturing
              Practices standards required by the FDA, the TPD and the
              equivalent Regulatory Authority elsewhere in the Territory, and
              the applicable regulations, policies or guidelines of each of them
              in effect for the manufacture and testing of pharmaceutical
              materials, active ingredients, or excipients, as applicable.

      1.1.7   "Clinical Activity" and "Clinical Activities" mean any one or more
              of the activities associated with drug testing in humans,
              including trial design and execution, payment of investigators',
              institutional, and contractors' fees, drug distribution and
              accountability, analytical testing, data management, statistical
              analysis, adverse event reporting, and scientific publication,
              performed or to be performed by the Parties or their
              Representatives in pursuit of the Development of the Product or
              post-Regulatory Approval commercialization of the Product.

      1.1.8   "Code" or "Codes" means the Code on Interactions with Healthcare
              Professionals promulgated by the Pharmaceutical Research and
              Manufacturers of America (PhRMA) and the American Medical
              Association (AMA) Guidelines on Gifts to Physicians from Industry,
              as either of the foregoing may be amended from time to time.

      1.1.9   "Commercially Reasonable Efforts" means efforts which are not less
              than those efforts a Party makes with respect to other
              pharmaceutical products in its portfolio (but, in any event, not
              less than the efforts that would be exerted by a reasonably
              prudent and diligent pharmaceutical company similarly situated and
              seeking to accomplish similar objectives),

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.


<PAGE>
                                       5


              taking into account the product's market potential, level of
              competition, number of prescribers and other relevant factors.

      1.1.10  "Compendium Listing" means the listing in any two or more
              publications or directories including Drugdex Information Service,
              AHFS Drug Information, or US Pharmacopoeia Drug Information,
              recognized by the US government for coverage under Medicaid,
              Medicare or other like health insurance programs, for use of VSLI
              in the treatment of Firstline NHL.

      1.1.11  "Confidential Information" means:

              (a)       all proprietary information and materials, patentable or
                        otherwise, of a Party which is disclosed in writing by
                        or on behalf of such Party to the other Party and marked
                        as confidential or proprietary, including DNA sequences,
                        vectors, cells, substances, formulations, techniques,
                        methodology, equipment, data, reports, know-how,
                        preclinical and clinical trials and the results thereof,
                        sources of supply, patent positioning, marketing plans
                        and business plans, including any negative developments;

              (b)       any other information, oral or written, designated in
                        writing by the disclosing Party to the other Party as
                        confidential or proprietary within ten (10) days after
                        such disclosure, whether or not related to the making,
                        use, importing or selling of the Product; and

              (c)       the Data, the Inex Technology, the Regulatory Approvals
                        and Regulatory Submissions, and the Licensed Patents
                        (all of which are deemed to be Confidential Information
                        of Inex);

              provided that Confidential Information shall not include such
              information which:

              (d)       was known or used by the receiving Party or its
                        Affiliates prior to its date of disclosure to the
                        receiving Party, as evidenced by the prior written
                        records of the receiving Party or its Affiliates; or

              (e)       either before or after the date of the disclosure to the
                        receiving Party is lawfully disclosed to the receiving
                        Party or its Affiliates by an independent, unaffiliated
                        Third Party rightfully in possession of the Confidential
                        Information; or

              (f)       either before or after the date of the disclosure to the
                        receiving Party becomes published or generally known to
                        the public through no fault or omission on the part of
                        the receiving Party or its Affiliates; or

              (g)       the receiving Party can verify, by written
                        documentation, results from research and development by
                        the receiving Party or any of its Affiliates independent
                        of disclosure by the other Party thereof.

      1.1.12  "Co-Promotion Agreement" means the Co-Promotion Agreement between
              Inex and Enzon of even date herewith.

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       6


      1.1.13  "Data" has the meaning set out in Section 10.3.2.

      1.1.14  "DDMAC Activities" mean all jointly agreed-to activities performed
              or to be performed by one or both Parties in accordance with the
              requirements of the Division of Drug Marketing, Advertising and
              Communications, Center for Drug Evaluation and Research of the
              FDA, and the Office of the Inspector General of the Department of
              Health and Human Services of the United States.

      1.1.15  "Development" means:

              (a)       all activities set forth in the Development Plan; and

              (b)       all activities necessary to obtain and maintain
                        Regulatory Approvals in each country in the Territory;

              including Development Clinical Activities, Regulatory Activities
              and Technical and Manufacturing Support Activities.

      1.1.16  "Development Clinical Activities" has the meaning set out in
              Section 5.2.

      1.1.17  "Development Costs" means, with respect to Development of the
              Product in respect of the Territory:

              (a)       the Development FTE Costs and Out-of-Pocket Costs
                        utilized or incurred by a Party in fulfilling its
                        obligations under the then-current Development Plan;

              (b)       all Development FTE Costs and Out of Pocket costs
                        incurred in excess of the budget in the then-current
                        Development Plan, provided that any such excess costs
                        have been approved in advance by the Joint Steering
                        Committee; and

              (c)       the Manufacturing Cost of Product produced for the
                        Development.

              For greater certainty, Development Costs do not include
              Commercialization Costs as defined in the Product Supply
              Agreement.

      1.1.18  "Development FTE" means a scientific or technical person employed
              by a Party or a Party's Affiliates and assigned to work on
              Development with such time and effort to constitute one person
              working on Development on a full time basis consistent with normal
              business and scientific practice (e.g., having appropriate
              education, training and experience and working *** hours per year
              of dedicated effort).

      1.1.19  "Development FTE Costs" means the price of Development FTEs to be
              used for the purposes of determining the costs incurred with
              respect to personnel performing work on the Development in
              accordance with the then-approved Development Plan. The price per
              Development FTE shall initially be *** per Development FTE year or
              pro-rata portion thereof incurred on the Development. The
              Development FTE rate includes all the fully burdened cost of
              salary, employee benefits, incidental materials, travel, lodging
              and other expenses including support staff and direct and indirect
              overhead for or associated with a Development FTE. On each
              anniversary of the Effective Date, the FTE rate shall be

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.


<PAGE>
                                       7


              raised by a percentage equal to the percentage increase in the
              Index (defined below) for the twelve (12) month period ending with
              December of the calendar year immediately preceding such
              anniversary date (such increase, the "CPI Increase"). For purposes
              of this Agreement, the term "Index" shall mean the Consumer Price
              Index for all Urban Consumers (CPI-U) - - U.S. City Average. All
              Items (1982-1984 = 100), as published by the United States Bureau
              of Labor Statistics, or if such index is no longer published, then
              the index most comparable thereto.

      1.1.20  "Development Plan" means the Development Plan for obtaining and
              maintaining Regulatory Approvals for the Product in the Territory,
              together with a corresponding budget accounting for the
              anticipated Development Costs to be expended or incurred by each
              Party in conducting the Development. The definitive Development
              Plan adopted in accordance with Section 4.4 will form a part of
              this Agreement.

      1.1.21  "Dollar" and "$" means United States Dollars.

      1.1.22  "Effective Date" means the date shown on page one of this
              Agreement.

      1.1.23  "Elan" means Elan Pharmaceuticals, Inc.

      1.1.24  "Elan Consent" means the consent by Elan to the execution and
              delivery of the Related Agreements and the subsequent grant of
              manufacturing rights contemplated herein.

      1.1.25  "Elan Improvements" has the meaning set out therefor in the Elan
              License.

      1.1.26  "Elan License" means the Amended and Restated License Agreement
              made as of April 3, 2003 between Elan, IE Oncology Company Limited
              and Inex Pharmaceuticals Corporation.

      1.1.27  "Elan Patents" means the Patents set out in Exhibit 1.1.27.

      1.1.28  "FDA" means the United States Food and Drug Administration or any
              successor thereto.

      1.1.29  "Field" means VSLI for all indications in humans.

      1.1.30  "First Commercial Sale" means (a) with respect to a country in the
              Territory, the first sale by Enzon, its sublicensees or Affiliates
              for use, consumption or resale of the Product in such country
              (excluding any sales for clinical trials, compassionate uses or
              other non-commercial purposes) and (b) with respect to the
              Territory, the First Commercial Sale in any country within the
              Territory. A sale to a sublicensee or an Affiliate shall not
              constitute a First Commercial Sale unless the sublicensee or
              Affiliate is the end user of the Product.

      1.1.31  "Firstline NHL" means the treatment of aggressive non-Hodgkin's
              lymphoma in patients not previously treated for aggressive
              non-Hodgkin's lymphoma.

      1.1.32  "GCP Requirements" or "Good Clinical Practices" means the then
              current standards for clinical trials for pharmaceuticals as
              required by the FDA, the TPD and the equivalent Regulatory
              Authority elsewhere in the Territory, and as applicable, the
              policies and

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       8


              guidelines of the International Conference on Harmonization in
              effect for the clinical testing of pharmaceutical materials.

      1.1.33  "GLP Requirements" or "Good Laboratory Practices" means the
              current Good Laboratory Practices standards required by the FDA,
              the TPD and the equivalent Regulatory Authority elsewhere in the
              Territory in effect for the testing of pharmaceutical materials as
              applied to raw materials and finished products.

      1.1.34  "include" and "including" (and the like) means "including, without
              limitation".

      1.1.35  "IND" means an Investigational New Drug application in accordance
              with the rules and regulations of the FDA.

      1.1.36  "Inex Patents" means the Patents set out in Exhibit 1.1.36.

      1.1.37  "Inex Technology" means all technical information and know-how
              owned or controlled by Inex which relates to the Product and is
              necessary or useful for the development and commercialization of
              the Product, and shall include:

              (a)       as of the Effective Date, all biological, chemical,
                        pharmacological, toxicological, clinical, assay, control
                        and manufacturing data and any other information owned
                        or controlled by Inex and necessary or useful for the
                        development and commercialization of the Product;

              (b)       any Data referred to in Section 10.3; and

              (c)       any Data referred to in Section 12.3 of the Product
                        Supply Agreement.

      1.1.38  "Intellectual Property Rights" means any rights to any Patents and
              copyrights and registrations and applications for registration of
              the foregoing rights, and trade secrets and moral rights.
              "Intellectual Property Rights" do not include trademark, domain
              name or trade name rights.

      1.1.39  "Joint Steering Committee" means the committee formed pursuant to
              Article 6. The Joint Steering Committee formed under this
              Agreement shall be the same as the Joint Steering Committee formed
              under the Product Supply Agreement.

      1.1.40  "Licensed Patents" means the Patents owned or controlled by Inex
              relating to VSLI, and necessary or useful for the development and
              commercialization of the Product, and shall include:

              (a)       as of the Effective Date, the Inex Patents and the Elan
                        Patents;

              (b)       to the extent of Inex's legal right to grant rights to
                        same, as of the Effective Date, the Regents' Patents;

              (c)       any Patents on inventions referred to in Section 10.3;
                        and

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       9


              (d)       any Patents on inventions referred to in Section 12.3 of
                        the Product Supply Agreement.

      1.1.41  "NDA" means a New Drug Application in accordance with the rules
              and regulations of the FDA.

      1.1.42  "NHL" means non-Hodgkin's Lymphoma.

      1.1.43  "not to be unreasonably withheld" and the like means not to be
              unreasonably withheld or delayed.

      1.1.44  "Out-of-Pocket Cost" means an out-of-pocket payment made by a
              Party or its Representatives to a Third Party but only to the
              extent such payment relates to costs which are incurred by a Party
              or its Representatives with respect to fulfilling its obligations
              under the Development Plan.

      1.1.45  "Party" means Inex or Enzon and "Parties" means Inex and Enzon.

      1.1.46  "Patent" means (a) all patent applications filed or having legal
              force in any country; (b) all patents that have issued or in the
              future issue therefrom, including without limitation utility,
              model and design patents and certificates of invention; and (c)
              all divisionals, continuations, continuations-in-part, reissues,
              renewals, extensions (including supplemental protection
              certificates), additions, registrations or confirmations to or of
              any such patent applications and patents.

      1.1.47  "Person" means and includes any individual, corporation,
              partnership, firm, joint venture, syndicate, association, trust,
              government body, and any other form of entity or organization.

      1.1.48  "Permitted Exception" means any or all of the following:

              (a)       any termination of the license between ***and the *** by
                        either *** or the *** before or after the Effective
                        Date; or

              (b)       any inability of IE Oncology Company Limited or Inex to
                        grant sublicenses under the *** License, or the absence
                        of a consent to such sublicense from *** or the ***; or

              (c)       any inability of *** to grant Intellectual Property
                        Rights under the ***to IE Oncology Company Limited
                        ("IE"), or of IE to grant such rights to Inex, or of
                        Inex to grant such rights to Enzon, which rights in each
                        case are at least co-extensive (within the Field and
                        within the Territory as defined in the Related
                        Agreements) with the scope of Intellectual Property
                        Rights under the *** purported to be granted by *** to
                        IE pursuant to the *** License;

              or the like respecting the ***.

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       10


      1.1.49  "Pharmacovigilance" means all the activities associated with
              maintaining an effective drug safety monitoring system and adverse
              events reporting system in compliance with the requirements of
              Regulatory Authorities.

      1.1.50  "Post-Approval Clinical Activities" has the meaning set out in
              Section 5.3.

      1.1.51  "Prime Rate" means the prime or equivalent rate quoted by
              Citibank, N.A. from time to time.

      1.1.52  "Product" means VSLI.

      1.1.53  "Product Supply Agreement" means the agreement for the supply of
              the Product from Inex to Enzon entered into as of the Effective
              Date.

      1.1.54  "QA" means Quality Assurance, being that part of each management
              system, within Inex and Enzon separately, having responsibility
              for assuring the quality of the Product in respect of compliance
              with Regulatory Requirements.

      1.1.55  "Quality/Technical Agreement" has the meaning set out in the
              Product Supply Agreement.

      1.1.56  ***

      1.1.57  "Regulatory Activity" and "Regulatory Activities" mean any one or
              more of the regulatory activities to be performed by the Parties,
              or their Representatives in pursuit of the Development of the
              Product, including writing, translation, compilation,
              notification, submission, filing, defense, maintenance and renewal
              of Regulatory Approvals and payment of fees associated therewith,
              and meeting with Regulatory Authorities.

      1.1.58  "Regulatory Approvals" means all necessary and appropriate
              regulatory approvals which must be obtained before placing the
              Product on the market in the Field in any country in the Territory
              in which such approval is required, including without limitation,
              INDs, NDAs, and any other comparable terms as applicable with
              regard to any such approvals in any other country in the
              Territory.

      1.1.59  "Regulatory Authority" or "Regulatory Authorities" means:

              (a)       the FDA, the TPD and any other like governmental
                        authorities, whether federal, provincial, state or
                        municipal, regulating the importation, distribution,
                        marketing and/or sale of therapeutic substances in the
                        Territory; and

              (b)       the corresponding governmental authorities, whether
                        federal, provincial, state or municipal, of each other
                        applicable jurisdiction outside the Territory in which
                        the Product will be developed, used or sold.

      1.1.60  "Regulatory Requirements" means:

              (a)       Applicable Laws, rules, regulations, guidances, and the
                        Codes and Standards in respect of all activities of the
                        Parties and their permitted Representatives under

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       11


                        the Related Agreements, including guidances in respect
                        of quality control and QA procedures and processes,
                        manufacturing and production batch records (including
                        the Master Production Record), packaging, handling,
                        storage, delivery and retention of raw material and
                        Product samples and associated support data, and all
                        licenses, certificates, authorizations or requirements
                        from Regulatory Authorities; and

              (b)       the corresponding laws, rules, regulations and guidances
                        of each other applicable jurisdiction outside the
                        Territory in which such activities take place.

      1.1.61  "Regulatory Submissions" means all submissions and filings made in
              furtherance of obtaining and maintaining any Regulatory Approvals.

      1.1.62  "Related Agreements" means, collectively, this Agreement, the
              Product Supply Agreement, the Quality/Technical Agreement and the
              Co-Promotion Agreement.

      1.1.63  "Representatives" means, in respect of a Party, that Party's
              Affiliates and their respective directors, officers, employees,
              consultants, subcontractors, sublicensees, agents, representatives
              and other persons acting under their authority.

      1.1.64  "Standards" means the Accreditation Council for Continuing Medical
              Education (ACCME) Standards for Commercial Support of Continuing
              Medical Education, as they may be amended from time to time.

      1.1.65  "Sublicensee" means a Third Party which is not an Affiliate of
              Enzon and to whom Enzon has granted a sublicense for the purpose
              of developing, using, selling, having sold, distributing,
              importing or exporting the Product in one or more countries of the
              Territory.

      1.1.66  "Technical and Manufacturing Support Activity" or "Technical and
              Manufacturing Support Activities" mean any one or more of the
              activities to be performed by the Parties or their Representatives
              in the area of analytical development, process development,
              manufacturing, and quality control, in pursuit of manufacturing
              scale-up and the Regulatory Approvals of the Product, including
              the design, testing, analysis, qualification, and validation of
              methods, equipment and/or processes.

      1.1.67  "Term" has the meaning set out in Section 11.1.

      1.1.68  "Territory" means Canada, Mexico and the USA.

      1.1.69  "Third Party(ies)" means any Person other than Inex or Enzon or an
              Affiliate of either of them.

      1.1.70  "TPD" means the Therapeutic Products Directorate Organization of
              Health Canada.

      1.1.71  "Trademarks" means trademarks, trade names, and domain names
              identified in Exhibit 1.1.71 and all applications and
              registrations thereof in the Territory.

      1.1.72  "USA" means the United States of America, including its
              territories, possessions and the Commonwealth of Puerto Rico.

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       12


      1.1.73  "Valid Claim" means either:

              (a)       a claim of an issued and unexpired patent which has not
                        been held unenforceable, unpatentable or invalid by a
                        court or other governmental agency of competent
                        jurisdiction, and which has not been admitted to be
                        invalid or unenforceable through reissue, disclaimer or
                        otherwise; or

              (b)       a claim in a patent application, provided that if such
                        pending claim has not issued as a claim of an issued
                        patent within seven years after the national filing date
                        of such patent application in a country, such pending
                        claim shall not be a Valid Claim for purposes of this
                        Agreement.

              In the event that a claim of an issued patent is held by a court
              or other governmental agency of competent jurisdiction to be
              unenforceable, unpatentable or invalid, and such holding is
              reversed on appeal by a higher court or agency of competition
              jurisdiction, such claim shall be reinstated as a Valid Claim
              hereunder.

      1.1.74  "Vincristine" means the chemical compound known as vincristine
              sulfate.

      1.1.75  "Vincristine Sulfate Liposomes Injection" or "VSLI" means
              Vincristine encapsulated in sphingomyelin/cholesterol liposomes or
              a kit for production of same.

1.2   Entire Agreement; Conflicts

The Parties hereby agree that, except as expressly modified hereby, the
following Articles of the Product Supply Agreement shall be part of this
Agreement as if set out herein: Sections 12.6 through 12.10 inclusive, Articles
13, 14, 15 and 16. This Agreement, together with the other Related Agreements,
constitutes the entire agreement between the Parties concerning the subject
matter hereof. In the event of a conflict between the terms and conditions set
out in any of the Related Agreements, the following agreements shall govern in
the following priority:

      1.2.1   the Product Supply Agreement;

      1.2.2   the Quality/Technical Agreement;

      1.2.3   this Development Agreement; and

      1.2.4   the Co-Promotion Agreement

1.3   Governing Law

This Agreement shall be governed by and construed in accordance with the laws of
Delaware in force therein without regard to its conflict of law rules.

1.4   Headings

The headings contained in this Agreement are for convenience of reference only
and shall not be considered in construing this Agreement. References to Articles
are references to Articles of this

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       13


Agreement and the Sections contained therein, and references to Sections are
references to Sections of this Agreement.

1.5   Severability

If a court or other tribunal of competent jurisdiction should hold any term or
provision of this agreement to be excessive, invalid, void or unenforceable, the
offending term or provision shall be deemed inoperative to the extent it
conflicts with such holding and shall be deemed to be modified to the extent
necessary to conform with such statute or rule of law, while still preserving,
to the extent practicable, the legitimate aims of the Parties, provided that the
remaining portions hereof shall remain in full force and effect. In the event
that the terms and conditions of this Agreement are materially altered as a
result of the above, the Parties will renegotiate the terms and conditions of
this Agreement to resolve any inequities.

                   Article 2 Grant and Reservation of Rights

2.1   Grant of Licenses

In furtherance of the Product Supply Agreement, and subject to the reservation
set forth in Section 2.2 of this Agreement, Inex hereby grants to Enzon:

      2.1.1   an exclusive license for the Field in the Territory under the Inex
              Patents;

      2.1.2   subject to the terms, conditions and limitations set out in the
              ***, an exclusive sublicense for the Field in the Territory under
              the ***;

      2.1.3   subject to Section Error! Reference source not found., to the
              extent of Inex's legal right to grant same, a non-exclusive
              sublicense for the Field in the Territory under the ***;

      2.1.4   an exclusive license for the Field in the Territory under the Inex
              Technology; and

for the sole purpose of developing (solely in accordance with the Development
Plan), using, selling, having sold, offering for sale, distributing, importing
and exporting the Product for the Field in the Territory, including the right to
grant sublicenses under these rights in accordance with Section 2.4. Enzon shall
not use or exploit for any purpose of any Licensed Patents or Inex Technology
except as permitted in this Agreement.

2.2   Reservation of Rights

      2.2.1   Except as otherwise expressly licensed to Enzon hereunder, Inex
              may exploit the Licensed Patents and Inex Technology for any
              purpose, including using, making, having made, selling, having
              sold, distributing and importing the Product:

              (a)       outside the Territory;

              (b)       inside the Territory but outside the Field;

              (c)       inside the Territory and inside the Field, for the
                        purpose of sales to Enzon; and

              (d)       in accordance with Section 11.3.

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       14


      2.2.2   Inex retains the non-exclusive (non-sublicensable, except as
              contemplated herein) right under the Licensed Patents and the Inex
              Technology:

              (a)       to practice the Licensed Patents and the Inex Technology
                        for internal research purposes for the Field;

              (b)       to Co-Promote the Product in the Territory in accordance
                        with the Co-Promotion Agreement; and

              (c)       to undertake Development as contemplated herein.

      2.2.3   For avoidance of doubt, Inex may exploit the Licensed Patents and
              Inex Technology in any territory for any liposomal product which
              does not contain Vincristine.

2.3   ***

2.4   Sublicenses

      2.4.1   Enzon shall have the right to sublicense all the rights granted in
              Section 2.1 to its Affiliates. Enzon hereby unconditionally
              guarantees the performance of any such Affiliates hereunder as if
              they were signatories to this Agreement to the extent the
              performance or lack of performance is a breach of this Agreement.
              A breach by any such Affiliate of any such obligation shall
              constitute a breach by Enzon of this Agreement and shall entitle
              Inex to exercise its rights hereunder, in addition to any other
              rights and remedies to which Inex may be entitled.

      2.4.2   Enzon shall also have the right to sublicense all the rights
              granted in Section 2.1 to Third Parties, subject to the following:

              (a)       Prior to the execution of any sublicense, Enzon shall
                        provide Inex with at least the following information
                        with respect to each potential Sublicensee: (i) the
                        identity of the Sublicensee; (ii) the territory in which
                        the Product will be sold; and (iii) a copy of the draft
                        sublicense.

              (b)       Each sublicense shall contain covenants by the
                        Sublicensee for the benefit of Inex to observe and
                        perform similar terms and conditions to those in this
                        Agreement. All sublicenses granted by Enzon shall be
                        personal to the Sublicensee and shall not be further
                        sublicensable or assignable without the prior written
                        consent of Inex. Such sublicenses shall terminate upon
                        the termination of Enzon's rights granted herein unless
                        events of default are cured by Enzon or Sublicensee
                        within sixty (60) days after notification by Inex of
                        default and/or as provided by the terms of this
                        Agreement.

              (c)       Enzon may grant such sublicenses only with the prior
                        written consent of Inex, which shall not be unreasonably
                        withheld.

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       15


              (d)       Unless otherwise agreed in the Elan Consent, Enzon may
                        grant such sublicenses only with the prior written
                        consent of Elan, which consent may be withheld in Elan's
                        absolute discretion.

              (e)       Any Sublicensee which wishes to grant a further
                        sublicense shall comply with the terms of this Section
                        as if the further sublicense were a sublicense
                        hereunder, including providing to Enzon and Inex the
                        information described in this Section with respect to
                        each potential sub-sublicensee, and obtaining the
                        consent referred to in this Section, prior to the
                        execution of any such sub-sublicense.

              (f)       In the event that Enzon becomes aware of a material
                        breach of any such sublicense by the Sublicensee, Enzon
                        shall promptly notify Inex of the particulars of same
                        and take all reasonable steps to enforce the terms of
                        such sublicense. Enzon shall remain responsible to Inex
                        for the compliance of each such Sublicensee with the
                        financial and other obligations due under this
                        Agreement. Upon the request of Inex, Enzon shall act
                        reasonably in considering any request of Inex for Enzon
                        to terminate such sublicense.

                  Article 3 Milestone Payments for Development

3.1   Signing and Regulatory Milestone Payments

As payments to facilitate the development of the Product and the establishment
of Inex's manufacturing and commercialization business, and as consideration for
the rights granted by Inex to Enzon under this Agreement, Enzon shall make the
following signing and regulatory milestone payments to Inex:

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

   Milestone:                                                        Payment:
--------------------------------------------------------------------------------

      3.1.1   Execution of the Product Supply Agreement,           $12.0 million
              this Agreement and the Co-Promotion Agreement

      3.1.2   NDA Accelerated Approval ("AA") in the USA within    $20.0 million
              eighteen (18) months of completed NDA submission
              date

      3.1.3   ***                                                  $***

      3.1.4   ***                                                  $***

      3.1.5   ***                                                  $***

      3.1.6   ***                                                  $***

      3.1.7   ***                                                  $***

      3.1.8   ***                                                  $***

      3.1.9   ***                                                  $***
================================================================================

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       16


Provided that:

      3.1.10  Enzon shall make the milestone payment referred to in Section
              3.1.1 to Inex on execution and delivery of this Agreement by the
              Parties, in payment for Inex's prior development work and other
              rights granted herein;

      3.1.11  Enzon shall make the milestone payments other than the ones
              referred to in Sections 3.1.1 and Error! Reference source not
              found. to Inex within thirty (30) days after achievement of each
              milestone by a Party, or by an Affiliate or a Sublicensee;

      3.1.12  Enzon shall make the milestone payments referred to in Section
              Error! Reference source not found. to Inex on the dates set out
              for occurrence of such milestone in Section Error! Reference
              source not found.;

      3.1.13  except for the payments set out in Section Error! Reference source
              not found., each milestone payment hereunder shall be made only
              one time, based upon the Product achieving a particular milestone
              regardless of how many times such milestone is achieved;

      3.1.14  only one of the three alternative milestone payments referred to
              in Sections 3.1.2, Error! Reference source not found. and Error!
              Reference source not found. will be paid;

      3.1.15  payment shall not be owed for a milestone which is not reached;

      3.1.16  except as expressly set out in this Agreement, each payment shall
              be made without setoff, deduction or similar right;

      3.1.17  with the exception of payment referred to in Section 3.1.9, which
              is creditable in accordance with its terms, any milestone payment
              described herein shall be non-refundable and non-creditable
              against any other payment due from Enzon to Inex under this
              Agreement;

      3.1.18  ***

      3.1.19  ***

      3.1.20  ***

      3.1.21  ***

      3.1.22  ***

3.2   Withholding Taxes

The Parties contemplate that there will be no payment or withholding by Enzon of
taxes on any payments made by Enzon to Inex pursuant to this Agreement. In the
event that either Party takes any action, or if the circumstances applicable to
either Party change with the result that taxes must be paid or withheld on the
payments due pursuant to this Agreement, then such taxes shall be borne by such
Party. Without limiting the generality of the foregoing:

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       17


      3.2.1   if Enzon assigns or sublicenses its rights hereunder, undergoes a
              reorganization or otherwise changes its structure, or changes its
              domicile, and thereafter taxes must be paid or withheld on the
              payments hereunder, such payments shall be grossed up so that Inex
              receives the actual amounts set out in this Agreement; and

      3.2.2   if Inex assigns or sublicenses its rights hereunder, undergoes a
              reorganization or otherwise changes its structure, or changes its
              domicile, and thereafter taxes must be paid or withheld on the
              payments hereunder, then such tax or withholding payments shall be
              deducted from the amounts set forth herein, and Enzon shall assist
              Inex as may be reasonably required, including providing proof of
              such payment of such tax payment, in order to allow Inex to claim
              the benefit of, exemption from or repayment such tax payment, as
              may be applicable; and

      3.2.3   in the event that payment or withholding by Enzon of taxes becomes
              necessary on any payments made by Enzon to Inex pursuant to this
              Agreement when neither Section 3.2.1 nor Section 3.2.2 applies,
              then such tax or withholding payments shall be deducted from the
              amounts set forth herein, and Enzon shall assist Inex as may be
              reasonably required, including providing proof of such payment of
              such tax payment, in order to allow Inex to claim the benefit of,
              exemption from or repayment such tax payment, as may be
              applicable.

Notwithstanding the foregoing, if Inex is able to credit the grossed up portion
of any payment made by Enzon pursuant to Section 3.2.1 against taxes payable by
Inex, or gain exemption from or repayment of such tax payment, Inex will
promptly pay the equivalent of the benefit received by Inex to Enzon.

3.3   Late Payments

Any payment by Enzon or Inex that is not paid on or before the date such payment
is due under this Agreement shall bear interest at a rate equal to the lesser
of:

      3.3.1   Prime Rate plus *** per year, or

      3.3.2   the maximum rate permitted by law;

calculated based on the number of days that payment is delinquent.

                             Article 4 Development

4.1   Development Activities in accordance with the Development Plan

Inex and Enzon will undertake Development as set out in the Development Plan and
as amended from time to time by the Parties in accordance with this Article 4.
Subject to Sections 5.2 and 5.8, from the Effective Date until the Parties'
agreement to the terms of the definitive Development Plan, Inex and Enzon will
undertake the Development acting reasonably. If either Party fails to perform
its responsibilities under the Development Plan (the "Non-performing Party")
after reasonable notice of such failure from the other Party (the "Performing
Party"), the Performing Party's sole remedy shall be that the Performing Party
may assume conduct of such responsibilities and the Development Plan shall be
amended to reflect such change. The cost of any such responsibilities so assumed
shall be borne by the Parties as set out in this Agreement.

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       18


4.2   Overview of Development

The Parties intend to work cooperatively to pursue the Development in accordance
with the terms of this Agreement. Unless otherwise set out in this Agreement,
the Parties will conduct the Development as directed by the Joint Steering
Committee and in conformance with the Development Plan. The Parties shall
collaborate closely, through the Joint Steering Committee, to assign
responsibility for conducting the various aspects of such Development. Unless
otherwise agreed by the Parties, the Parties will conduct the activities
assigned to them in the Development Plan.

4.3   Development Diligence

      4.3.1   Inex shall make its third submission to the FDA for an NDA for the
              Product as soon as reasonably possible.

      4.3.2   Each of the Parties, directly and through its permitted
              Representatives, shall use Commercially Reasonable Efforts to
              Develop the Product for the USA and Canada, including carrying out
              its respective responsibilities under the Development Plan,
              including to:

              (a)       conduct or cause to be conducted the necessary and
                        appropriate clinical trials as necessary to obtain and
                        maintain Regulatory Approvals for the Product; and

              (b)       prepare, file and prosecute or cause to be prepared,
                        filed and prosecuted the Regulatory Submissions for the
                        Product in the USA and Canada.

      4.3.3   Each of the Parties, directly and through its permitted
              Representatives, shall perform the Development in compliance with
              Regulatory Requirements.

      4.3.4   Each Party shall ensure none of its Representatives who
              participate in any activities under the Related Agreements:

              (a)       is or has been suspended, debarred or disqualified by
                        the FDA;

              (b)       has been convicted of any offence that would form the
                        basis for any debarment; or

              (c)       is or has been subject to any proceedings for the
                        suspension, disqualification or debarment of such Party
                        or any Representative of such Party.

4.4   Development Plans

      4.4.1   Within ninety (90) days after the Effective Date, the Joint
              Steering Committee shall prepare, review and submit to the Parties
              for approval a detailed Development Plan for the Development of
              the Product.

      4.4.2   Development of the Product shall be conducted by the Parties in
              conformance with the Development Plan.

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       19


      4.4.3   The Development Plan may be updated by the Joint Steering
              Committee and the Parties as provided herein.

      4.4.4   At a minimum, the Development Plan as amended from time to time
              shall describe the specific activities to be performed in the
              Territory for a twelve (12) month period, with a summary of
              development activities to be performed thereafter. The Development
              Plan will be reviewed on at least a semi-annual basis by the Joint
              Steering Committee to update the specific activities to be
              performed for the rolling twelve (12) month period, as well as to
              reflect the revised Development as the Joint Steering Committee
              reasonably determines to be necessary or useful. Notwithstanding
              the above, no amendment to any Development Plan shall be construed
              to be final unless it has been made in accordance with the
              provisions of Article 6.

4.5   Reports on Development

Each Party will keep the other Party fully informed on the progress of the
Development in respect of the Territory, using reasonable reporting requirements
mutually established by the Parties. As a minimum requirement, the Joint
Steering Committee shall receive and review and approve quarterly progress
reports.

4.6   Attendance at Regulatory Meetings

Each Party will inform the other Party of planned meetings between its
representatives and governmental or Regulatory Authorities regarding Regulatory
Approvals and Regulatory Submissions for the Product in the Territory and, where
appropriate to do so, make reasonable efforts to include the other Party in such
meetings.

4.7   Subcontractors

Either Party may subcontract to any of its Representatives any of its
obligations in respect of the Development with the consent of the other Party,
such consent not to be unreasonably withheld; provided however, that the
subcontracting Party shall be responsible for the performance of its
Representatives and shall remain fully responsible and obligated to the other
Party for all activities undertaken by its Representatives.

                Article 5 Development Responsibility and Funding

5.1   Shared Funding of Certain Development Costs

Each Party shall bear the initial responsibility for funding all Development
Costs required to support the conduct of all such Party's responsibilities in
pursuit of Regulatory Approvals for the Product in the Territory in accordance
with the Development Plan, subject to allocation and reimbursement for such
expenses in accordance with this Article 5.

5.2   Development Clinical Activities

      5.2.1   Subject to Section 5.2.2, Enzon will fund 50%, and Inex 50% of
              Development Costs for all the following Clinical Activities (the
              "Development Clinical Activities"):

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       20


              (a)       obtaining and maintaining Regulatory Approval for the
                        first label claim for the Product in each country in the
                        Territory, including any FDA mandated Phase III
                        confirmatory trials for the first label claim if VSLI
                        receives NDA Accelerated Approval in the USA;

              (b)       any jointly agreed-to trials designed to obtain
                        additional Regulatory Approvals for the Product in the
                        Territory;

              (c)       all Phase II clinical trials for the Product ongoing as
                        of the Effective Date, a listing of which is set out in
                        Exhibit 5.2.1(c); and

              (d)       all jointly agreed-to trials sponsored by either of the
                        Parties to explore new indications or dosing regimens
                        for the Product.

      5.2.2   Notwithstanding anything herein to the contrary, Enzon's
              contribution to Development Costs for Development Clinical
              Activities under this Section 5.2 from the Effective Date through
              June 30, 2004 shall be limited to *** of the first *** of
              Development Costs incurred. Inex shall pay *** of the Development
              Costs incurred during this period in excess of ***, if any.

5.3   Post-Approval Clinical Activities

Enzon will be responsible for and fund *** of the costs for all the following
Clinical Activities (the "Post-Approval Clinical Activities"):

      5.3.1   Clinical Activities typically associated with post-Regulatory
              Approval commercialization, including Phase IV clinical trials and
              post-Regulatory Approval Compendium Listings;

      5.3.2   physician-sponsored studies; and

      5.3.3   any Clinical Activities undertaken by the Parties not required by
              a Regulatory Authority in order to obtain any Regulatory Approval
              or as a condition of obtaining or maintaining a Regulatory
              Approval.

5.4   Regulatory Activities

      5.4.1   The Parties will coordinate their activities with each other with
              respect to the overall regulatory strategy for the Product in the
              Territory, and with respect to Inex's overall regulatory strategy
              for the Product outside the Territory.

      5.4.2   Inex will have primary responsibility for Regulatory Activities in
              the Territory, with Enzon's input and advice.

      5.4.3   Enzon will fund ***, and Inex *** of all Development Costs for
              Regulatory Activities associated with obtaining and maintaining
              Regulatory Approval for the Product in the Territory.

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       21


5.5   Filing of Regulatory Submissions

      5.5.1   Inex or an Affiliate of Inex designated by Inex shall be named as
              the applicant for all Regulatory Submissions and holder of all
              Regulatory Approvals in all countries, including the countries in
              the Territory, and all such Regulatory Approvals and Regulatory
              Submissions shall be owned as set out in Section 10.4.

5.6   Technical and Manufacturing Support Activities

      5.6.1   Each Party will have responsibility for Technical and
              Manufacturing Support Activities in the Territory as set out in
              the Development Plan, with input and advice from the other Party.

      5.6.2   Enzon will fund ***, and Inex *** of all Development Costs
              including Costs for Technical and Manufacturing Support Activities
              and the following additional activities, if mutually agreed upon,
              shall be Technical and Manufacturing Support Activities:

              (a)       manufacturing scale up activities;

              (b)       the contracting of secondary suppliers and testing
                        laboratories;

              (c)       the establishment of secondary manufacturing sites; and

              (d)       the establishment of secondary suppliers and/or
                        alternate sources of raw materials.

5.7   Funding of Development Costs

      5.7.1   From and after the Effective Date, in respect of each calendar
              quarter in which Development Costs are incurred, the Parties shall
              bear their proportionate share of Development Costs as set out in
              this Article.

      5.7.2   Within twelve Business (12) Days after of the end of each calendar
              quarter, each Party shall provide the other Party with a
              reasonably detailed invoice setting forth such Party's Development
              Costs.

      5.7.3   Such invoices shall be accompanied by appropriate documentation
              ("Supporting Documentation"), including a listing of expenditures
              in reasonably specific detail to support the Party's determination
              of the actual Development Costs incurred in conducting Development
              work during such calendar quarter.

      5.7.4   If the invoices and Supporting Documentation (as verified by the
              Joint Steering Committee) demonstrate that one Party, in
              completing tasks assigned for such quarter under the Development
              Plan (but excluding tasks each Party is to perform at its own
              expense hereunder) has borne more of the Development Costs than
              the share set out for such Party in this Article 5, then within 30
              days after the exchange of invoices and Supporting Documentation,
              there shall be an accounting and payment between the Parties to
              bring the Development Costs incurred by them respectively during
              such quarter into conformity with this Article 5.

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       22


      5.7.5   Each Party shall use Commercially Reasonable Efforts to comply
              with the applicable budget for each activity set out in the
              Development Plan for such Party during the each calendar year. In
              the event that a Party incurs any Development FTE Costs for a
              particular activity that exceed the amount budgeted therefor, such
              event shall not be considered a breach of this Agreement by such
              Party, but the other Party shall not be responsible for funding
              any such excess amount, unless otherwise agreed to in writing by
              the Parties. If a Party believes that completion of the assigned
              Development tasks will exceed the portion of such budget that is
              allocated for such Party's efforts, such Party will contact the
              Joint Steering Committee promptly after such determination in
              order to initiate discussion by the Joint Steering Committee of
              such matter and appropriate means of resolving same.

5.8   Transition

From the Effective Date until the Parties' agreement to the terms of the
definitive Development Plan, Inex and Enzon will fund their respective shares of
Development Costs incurred as contemplated by this Agreement. If the Parties
fail to agree on the terms of the definitive Development Plan within 90 days of
the Effective Date, until the terms of the definitive Development Plan are
determined, the Parties shall fund their respective shares of Development Costs
incurred by the Parties, acting reasonably. Notwithstanding the foregoing, after
the Effective Date, in the absence of a definitive Development Plan agreed upon
by the Parties, no more than an aggregate of US$*** in Development Costs will be
incurred without the review of the Joint Steering Committee and the agreement of
the Parties.

5.9   Records

Both Parties shall keep full, true and accurate books of accounts and other
records containing all information and data which may be necessary to ascertain
and verify:

      5.9.1   the Development Costs incurred by each of them and their
              respective Representatives for a period of three (3) years after
              the completion of the Development; and

      5.9.2   any other amount payable hereunder for a period of three (3) years
              after the completion of the Term.

5.10  Audits

      5.10.1  During the Development and for a period of one (1) year following
              the completion of the Development, Enzon shall have the right from
              time to time (not to exceed once during each calendar year) to
              have either its internal financial audit personnel or an
              independent firm of accountants (i.e., a certified public
              accountant or like person reasonably acceptable to Inex) inspect
              the books, records and supporting data of Inex referred to in
              Section 5.9. Such independent firm of accountants shall perform
              these audits at Enzon's expense upon reasonable prior notice and
              during Inex's regular business hours, and shall agree as a
              condition to such audit to maintain the confidentiality of all
              information disclosed or observed in connection with such audit
              and to disclose to Enzon only whether Inex has complied with its
              obligations under this Agreement with respect to Development
              Costs. If the result of such audit demonstrates an overpayment or
              underpayment, there shall be a prompt (but in no event more than
              60 days after

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       23


              completion of the audit) accounting between the parties to
              reconcile such overpayment or underpayment. If the result of such
              audit demonstrates an overpayment by Enzon of *** or more, Inex
              shall pay Enzon the reasonable costs of such audit.

      5.10.2  During the Term and for a period of one (1) year thereafter, Inex
              shall have the right from time to time (not to exceed once during
              each calendar year) to have either its internal financial audit
              personnel or an independent firm of accountants (i.e., a certified
              public accountant or like person reasonably acceptable to Enzon)
              inspect the books, records and supporting data of Enzon referred
              to in Section 5.9. Such independent firm of accountants shall
              perform these audits at Inex's expense upon reasonable prior
              notice and during Enzon's regular business hours, and shall agree
              as a condition to such audit to maintain the confidentiality of
              all information disclosed or observed in connection with such
              audit and to disclose to Inex only whether Enzon has complied with
              its obligations under this Agreement with respect to the payment
              of money owing pursuant to this Agreement. If the result of such
              audit demonstrates an overpayment or underpayment, there shall be
              a prompt (but in no event more than 60 days after completion of
              the audit) accounting between the parties to reconcile such
              overpayment or underpayment. If the result of such audit
              demonstrates an underpayment of *** or more, Enzon shall pay Inex
              the reasonable costs of such audit.

      5.10.3  The provisions of Sections 5.10.1 and 5.10.2 are based on the
              assumption that the net flow of payments under Section 5.7 will be
              from Enzon to Inex. If this assumption proves incorrect, the
              provisions of Sections 5.10.1 and 5.10.2 will be deemed modified
              to permit an appropriate accounting between Inex and Enzon to
              correct for any underpayment or overpayment by Inex.

                       Article 6 Joint Steering Committee

6.1   Joint Steering Committee

      6.1.1   As of the Effective Date of this Agreement, the Joint Steering
              Committee shall be formed and shall be constituted of four
              representatives from each Party. The members of the Joint Steering
              Committee as of the Effective Date are as set forth on Exhibit
              6.1. The Chairperson of the Joint Steering Committee at the first
              meeting of the Joint Steering Committee shall be an Enzon member
              of the Joint Steering Committee, and thereafter, the Chairperson
              will alternate at each meeting between a representative of Inex
              and a representative of Enzon. The Chairperson shall be
              responsible for issuing an agenda for the meeting, conducting and
              chairing the meeting and preparing the minutes for the meeting,
              and such other tasks as assigned by the committee. The Joint
              Steering Committee shall meet regularly at least quarterly during
              the period when Development in respect of the Territory is
              occurring, or more frequently if necessary.

      6.1.2   Each Party shall bear its own expenses associated with its
              participation in the Joint Steering Committee and its
              administration and oversight of the activities contemplated by the
              Agreement. Such expenses shall not be included in Development
              Costs.

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       24


6.2   Meetings of the Joint Steering Committee

      6.2.1   The Joint Steering Committee should meet at least once per year at
              the location of Inex or an Affiliate of Inex, and once per year at
              a location of Enzon or an Affiliate of Enzon. All other meetings
              of the Joint Steering Committee may occur by telephone, video
              conference or other acceptable means or location if requested by a
              Party. The Joint Steering Committee shall oversee all Development
              activities of the Parties under this Agreement, including
              coordinating the overall strategy for Development. The Joint
              Steering Committee shall have the responsibilities as set forth
              generally in Exhibit 6.1. Each Party may appoint its
              representatives to the Joint Steering Committee and other members
              of its project team at its discretion. It is the intent of the
              Parties to assign responsibilities for the various operational
              aspects of the Development Plan to those portions of their
              respective organizations which have the appropriate resources,
              expertise and responsibility for such functions. The Joint
              Steering Committee shall act only as a body making recommendations
              to the Parties, and neither Party is bound by any recommendation
              of the Joint Steering Committee. The members of the Joint Steering
              Committee shall attempt, in good faith, to reach consensus on all
              matters before the committee and make a consensus recommendation
              to the Parties. In the event that the Joint Steering Committee
              cannot make a consensus recommendation to the Parties which is
              acceptable to the Parties, either Party may refer the matter for
              resolution in accordance with the terms of Article 16 of the
              Product Supply Agreement.

      6.2.2   The Joint Steering Committee shall cause there to be recorded
              reasonably detailed minutes of its meetings. The Party providing
              the chairperson of each meeting shall be responsible for preparing
              draft minutes of such meeting and distributing same to the other
              members of the committee within five Business Days after such
              meeting. If the other Party desires to revise the draft minutes it
              will provide comments on such minutes within ten Business Days
              after receiving the minutes. If such comments are provided,
              members of the Joint Steering Committee designated by each Party
              shall confer promptly and in good faith to resolve such comments
              and finalize the minutes. If the members of the Joint Steering
              Committee are unable to finalize the minutes within 30 days after
              the date of the meeting, either Party may refer the matter for
              resolution in accordance with the terms of Article 16 of the
              Product Supply Agreement.

6.3   Working Committees

The Joint Steering Committee may establish working committees to manage actively
the Development. Such working committees will conduct at a minimum quarterly
planning and review meetings as well as ad hoc meetings as necessary. The
primary method of meeting will be teleconference. Responsibilities of the
working committees may include overseeing the planning and monitoring of the
clinical development process and the regulatory and commercialization processes.

                 Article 7 Pharmacovigilance, DDMAC and Recalls

7.1   Regulatory Responsibilities

Inex will be responsible for maintaining and fulfilling all Regulatory
Requirements with respect to the Product that are imposed upon Inex as the
manufacturer and holder of the Regulatory Approvals. Subject

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       25


to the other express terms of the Related Agreements, Enzon and its designees
will have sole responsibility for the advertising and other promotion of the
Product and for maintaining and fulfilling all Regulatory Requirements with
respect to the Product that are imposed upon Enzon as the advertiser, marketer
and distributor thereof.

7.2   Pharmacovigilance Agent

      7.2.1   Unless the Parties agree to establish the agency referred to in
              Section 7.2.2 on an accelerated basis, Inex shall be responsible
              for performing Pharmacovigilance in respect of all pre-Regulatory
              Approval Clinical Activities (in addition to all other Regulatory
              Activities for which Inex is responsible). Until this agency is
              established, if Enzon receives any information of any type
              whatsoever that may constitute a complaint regarding the Product
              or indicates that the Product in any way relates to an Adverse
              Drug Event, then it will record the information set forth on
              Exhibit 1.1.1 and transmit the completed form to Inex as soon as
              possible, and in any event at least in time to allow Inex to meet
              its reporting obligations under Regulatory Requirements. Inex will
              then report the Adverse Drug Event in accordance with Regulatory
              Requirements, and provide Enzon with a copy(ies) of all
              documentation provided to Regulatory Authorities in respect of
              such complaint or Adverse Drug Event. Further, until this agency
              is established, if Inex receives any information of any type
              whatsoever that may constitute a complaint regarding the Product
              or indicates that the Product in any way relates to an Adverse
              Drug Event, then it will record the information set forth on
              Exhibit 1.1.1, provide a copy of the completed form to Enzon (if
              possible, prior to submitting it to Regulatory Authorities) and
              report the Adverse Drug Event in accordance with Regulatory
              Requirements.

      7.2.2   After Regulatory Approval of the Products by a Regulatory
              Authority (or sooner if and to the extent agreed to by the
              Parties), Enzon shall be appointed by Inex as Inex's agent with
              respect to the regulatory dossier for the Product in the Field in
              the Territory for the sole purpose of conducting
              Pharmacovigilance. After this agency has been established, Enzon
              shall manage and carry out on behalf of Inex all relevant
              communications and relations with Regulatory Authorities to the
              extent related to Pharmacovigilance with respect to the Product.
              Inex shall be entitled to participate in all negotiations and
              discussions between Enzon and Regulatory Authorities relating to
              Pharmacovigilance with respect to the Product. Without limiting
              the generality of the foregoing, after this agency has been
              established, if Inex receives any information of any type
              whatsoever that may constitute a complaint regarding the Product
              or indicates that the Product in any way relates to an Adverse
              Drug Event, then it will record the information set forth on
              Exhibit 1.1.1 and transmit the completed form to Enzon as soon as
              possible, and in any event at least in time to allow Enzon to meet
              its reporting obligations under Regulatory Requirements. Enzon
              will then report the Adverse Drug Event in accordance with
              Regulatory Requirements, and provide Inex with a copy(ies) of all
              documentation provided to Regulatory Authorities in respect of
              such complaint or Adverse Drug Event. Further, after this agency
              has been established, if Enzon receives any information of any
              type whatsoever that may constitute a complaint regarding the
              Product or indicates that the Product in any way relates to an
              Adverse Drug Event, then it will record the information set forth
              on Exhibit 1.1.1, provide a copy of the completed form to Inex (if
              possible, prior to submitting it to Regulatory Authorities) and
              report the Adverse Drug Event in accordance with Regulatory
              Requirements.

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       26


7.3   Agency for DDMAC Activities

      7.3.1   Inex hereby appoints Enzon as its agent for the Product in the
              Field in the Territory for the sole purpose of conducting all
              DDMAC Activities in the USA and the foreign equivalents in the
              remainder of the Territory.

      7.3.2   Enzon shall perform the DDMAC Activities in the USA and the
              foreign equivalents in the remainder of the Territory in
              compliance with Regulatory Requirements.

      7.3.3   Enzon will perform all DDMAC Activities in the USA and the foreign
              equivalents in the remainder of the Territory and subject to
              Section 7.1, be responsible for all post-approval
              Pharmacovigilance activities, and assume all the costs associated
              therewith.

      7.3.4   In each country for which Inex is the holder of the Regulatory
              Approval, Enzon shall regularly inform Inex of Enzon's DDMAC
              Activities and foreign equivalents and obtain Inex's prior consent
              to Enzon's DDMAC Activities and foreign equivalents and plans
              respecting any of them. In the event Enzon informs Inex of its
              DDMAC Activities, foreign equivalents and plans, and does not
              receive a written objection from Inex within 10 Business Days,
              Inex shall be deemed to have consented to such activities and
              plans.

7.4   Agent for Regulatory Authorities Generally

      7.4.1   Nothing in Section 7.1 or this Section 7.4 precludes Inex from
              appointing an agent for Regulatory Authorities for products other
              than the Product, or for territories outside the Territory.

      7.4.2   All activities, communications and relations as well as Enzon's
              role as agent for Regulatory Authorities shall be performed by
              Enzon in close coordination with Inex, as holder of the Regulatory
              Approvals.

      7.4.3   In respect of all of the foregoing under Section 7.1 or this
              Section 7.4, except as required by Regulatory Requirements and
              except for those reporting requirements which have timeliness
              requirements that make it impossible to seek and obtain Inex's
              consent prior to making such report, any communications with
              Regulatory Authorities by Enzon under Section 7.1 or this Section
              7.4 are subject to the consent of the Inex, such consent not to be
              unreasonably withheld.

7.5   Recalls and Withdrawals of Product

      7.5.1   If Inex or Enzon will be required or requested by any Regulatory
              Authority to recall any Product for any reason, or should Enzon
              decide voluntarily to withdraw any Product:

              (a)       Enzon will be responsible for co-coordinating such
                        recall or withdrawal;

              (b)       Enzon shall pay the costs and expenses of such recall or
                        withdrawal, subject to recovery of some or all of same
                        in accordance with the terms of Section 7.5.2;

              (c)       unless Inex is liable for such costs and expenses in
                        accordance with the terms of Section 7.5.2, Enzon will
                        remain responsible to Inex for the Purchase Price for

<PAGE>
                                       27


                        such Product and will reimburse Inex for all of the
                        reasonable costs and expenses actually incurred by Inex
                        in connection with such recall or withdrawal including,
                        but not limited to, administration of the recall or
                        withdrawal and such other reasonable costs as may be
                        reasonably related to the recall or withdrawal; and

              (d)       both Parties will cooperate fully with one another in
                        connection with any such recall or withdrawal.

      7.5.2   if a recall or withdrawal is due to Inex's negligence, willful
              misconduct or breach of this Agreement or Inex's failure to
              Manufacture the Product in conformity with the Specifications or
              the provisions of the Product Supply Agreement or the
              Quality/Technical Agreement, Inex will reimburse Enzon for all of
              Enzon's reasonable costs and expenses actually incurred by Enzon
              in connection with the recall or withdrawal, including the
              Purchase Price for the recalled or withdrawn Product, costs of
              retrieving Product already delivered to customers, costs and
              expenses Enzon is required to pay for notification, shipping and
              handling charges, destruction or return of the defective Product
              or Product and such other reasonable costs as may be reasonably
              related to the recall or withdrawal.

      7.5.3   If the Parties are unable to agree on whether or not a recall or
              withdrawal is due to Inex's negligence, willful misconduct or
              breach of this Agreement, either Party may refer the matter for
              resolution pursuant to Article 16 of the Product Supply Agreement.

                       Article 8 Additional Opportunities

8.1   Pipeline Drug

For a reasonable period after the Effective Date, the Parties will make good
faith efforts to work together to identify and secure rights to one other
oncology or hematology product from within or to be added to Enzon's current
pipeline. The Parties' intention is that the development and commercialization
of such new product in the Territory would be on the basis of a 50:50 funding
and profit sharing split.

8.2   Legal Effect

The matters set forth in this Article 8 constitute merely an expression of the
desire of the Parties to negotiate with each other regarding the terms of an
agreement regarding the subject matter of this Article 8, and nothing in this
Article 8 will have any legal or binding effect unless set out in writing in a
separate agreement and signed by the duly authorized representatives of the
Parties.

                    Article 9 Representations and Warranties

9.1   By Enzon

Enzon hereby represents and warrants to Inex that, as of the Effective Date:

      9.1.1   Enzon has full legal right, power and authority to execute,
              deliver and perform its obligations under the Related Agreements;

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       28


      9.1.2   the execution, delivery and performance by Enzon of the Related
              Agreements does not contravene or constitute a default under any
              provision of Applicable Law or its articles or by-laws (or
              equivalent documents) or of any judgment, injunction, order,
              decree or other instrument binding upon Enzon;

      9.1.3   all licenses, consents, authorizations and approvals, if any,
              required for the execution, delivery and performance by Enzon of
              the Related Agreements have been obtained and to the best
              knowledge of Enzon are in full force and effect and all conditions
              thereof have been complied with, and, except for appropriate
              disclosure regarding the Related Agreements under the Securities
              Exchange Act of 1934, as amended, no other action by or with
              respect to, or filing with, any governmental authority or any
              other person or entity is required in connection with the
              execution, delivery and performance by Enzon of the Related
              Agreements;

      9.1.4   except for the Permitted Exception, to the best knowledge of
              Enzon, the exploitation by Enzon of the rights granted to Enzon
              hereunder in pursuit of the Development, Manufacture and
              Commercialization of the Product do not infringe the Intellectual
              Property Rights of any Third Party;

      9.1.5   assuming each is a valid, binding and enforceable agreement of
              Inex, each of the Related Agreements constitutes a valid and
              binding agreement of Enzon, enforceable against Enzon in
              accordance with its terms, except as such enforceability may be
              limited by bankruptcy, insolvency, moratorium or creditors' rights
              generally;

      9.1.6   the execution, delivery and performance by Enzon of each Related
              Agreement does not and will not conflict with or result in a
              material breach of any of the terms and provisions of any Third
              Party agreement of Enzon entered into as of the Effective Date;

      9.1.7   except for the Permitted Exception, Enzon is not aware of any
              impediment, including without limitation any Third Party agreement
              of Enzon, which would prevent Enzon from performing its
              obligations under the Related Agreements;

      9.1.8   Enzon will not enter into any Third Party agreement after the
              Effective Date which, in any way, will limit its ability to
              perform all of the obligations undertaken by Enzon under the
              Related Agreements; and

      9.1.9   except for Intellectual Property Rights owned by Elan and licensed
              to Enzon, Enzon does not own or control any Intellectual Property
              Rights which could be asserted against Inex for Inex's performance
              under the Related Agreements, or which could be infringed by the
              developing, using, selling, having sold, distributing and
              importing of the Product in the Territory.

9.2   By Inex

Inex hereby represents and warrants to Enzon that, as of the Effective Date:

      9.2.1   Inex has full legal right, power and authority to execute, deliver
              and perform its obligations under the Related Agreements;

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       29


      9.2.2   the execution, delivery and performance by Inex of the Related
              Agreements does not contravene or constitute a default under any
              provision of Applicable Law or its articles or by-laws (or
              equivalent documents) or of any judgment, injunction, order,
              decree or other instrument binding upon Inex;

      9.2.3   all licenses, consents, authorizations and approvals, if any,
              required for the execution, delivery and performance by Inex of
              the Related Agreements, including the Elan Consent, have been
              obtained and, except for the Permitted Exception, to the best
              knowledge of Inex, are in full force and effect and all conditions
              thereof have been complied with, and, except for appropriate
              disclosure regarding the Related Agreements required by any stock
              exchange having authority, except for the Permitted Exception, to
              the best knowledge of Inex no other action by or with respect to,
              or filing with, any governmental authority or any other person or
              entity is required in connection with the execution, delivery and
              performance by Inex of the Related Agreements;

      9.2.4   except for the Permitted Exception, and the rights granted by Inex
              outside the Field or outside the Territory, Inex is the exclusive
              owner or licensee of all legal and beneficial right, title and
              interest in and to the Licensed Patents;

      9.2.5   except for the Permitted Exception, Inex has the rights to the
              Elan Patents necessary to grant the sublicenses granted in the
              Related Agreements and the Elan License has not been breached by
              Inex or its Affiliates or, to the best knowledge of Inex, by Elan
              and its Affiliates;

      9.2.6   except for rights granted by Inex outside the Field or outside the
              Territory, Inex is the sole and exclusive owner or licensee of the
              Inex Technology, free and clear of any lien, claim or encumbrance
              or rights of any other person or entity;

      9.2.7   except for the Permitted Exception, to the best knowledge of Inex,
              the exploitation by Enzon of the rights granted to Enzon under the
              Related Agreements in pursuit of the Development, Manufacture and
              Commercialization of the Product do not infringe the Intellectual
              Property Rights of any Third Party;

      9.2.8   assuming each is a valid, binding and enforceable agreement of
              Enzon, each of the Related Agreements constitutes a valid and
              binding agreement of Inex, enforceable against Inex in accordance
              with its terms, except as such enforceability may be limited by
              bankruptcy, insolvency, moratorium or creditors' rights generally;

      9.2.9   the execution, delivery and performance by Inex of the Related
              Agreements does not and will not conflict with or result in a
              material breach of any of the terms and provisions of any Third
              Party agreement of Inex entered into as of the Effective Date;

      9.2.10  except for the Permitted Exception, Inex is not aware of any
              impediment, including without limitation any Third Party agreement
              of Inex, which would prevent Inex from performing its obligations
              under the Related Agreement;

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       30


      9.2.11  Inex will not enter into any Third Party agreement after the
              Effective Date which, in any way, will limit its ability to
              perform all of the obligations undertaken by Inex under the
              Related Agreements;

      9.2.12  except for the Licensed Patents and Inex Technology, Inex does not
              own or control any Intellectual Property Rights which could be
              asserted against Enzon for Enzon's performance under the Related
              Agreements, or which could be infringed by the developing, using,
              selling, having sold, distributing and importing of the Product in
              the Territory; and

      9.2.13  at the time delivered to Enzon, all Product:

              (a)       will fully conform to the Regulatory Requirements, the
                        Specifications and the Master Production Record; and

              (b)       will not, as the result of Inex's undertakings or
                        failure to perform its undertakings as set out in this
                        Agreement, be adulterated or misbranded within the
                        meaning of Section 501[351] and 502[352] of the Federal
                        Food, Drug and Cosmetic Act, as amended, and the
                        regulations issued thereunder or within the meaning of
                        any applicable state or local law, the adulteration and
                        misbranding provisions of which are similar to the
                        Federal Food, Drug and Cosmetic Act.

9.3   Survival of Representations and Warranties

The representations and warranties contained herein shall survive the execution,
delivery and performance of this Agreement by the Parties, notwithstanding any
investigation at any time made by or on behalf of any Party or Parties.

9.4   DISCLAIMER

EXCEPT FOR THE EXPRESS WARRANTIES AND REPRESENTATIONS CONTAINED IN THIS
AGREEMENT, NEITHER Inex NOR ENZON MAKES, AND EACH HEREBY EXPRESSLY DISCLAIMS,
ANY WARRANTIES OR REPRESENTATIONS, EITHER EXPRESS OR IMPLIED, WHETHER IN FACT OR
IN LAW, INCLUDING WITHOUT LIMITATION IMPLIED WARRANTIES OF MERCHANTABILITY OR
FITNESS FOR A PARTICULAR PURPOSE, OR VALIDITY OR SCOPE OR NON-INFRINGEMENT OF
ANY INTELLECTUAL PROPERTY RIGHTS.

                    Article 10 Intellectual Property Rights

10.1  Injunctive Relief

Each party acknowledges the competitive and technical value of the Licensed
Patents and Inex Technology, and the sensitive and confidential nature of the
Confidential Information and agrees that monetary damages alone will be
inadequate to protect the other party's interests against any actual or
threatened material breach of this Agreement. Accordingly, each party consents
to the granting of specific performance and injunctive or other equitable relief
to the other party in respect of any actual or threatened breach of this
Agreement, without proof of actual damages.

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       31


10.2  Ownership of Pre-Existing Intellectual Property Rights

Any Intellectual Property Rights or trademark rights owned by either Party prior
to the Effective Date shall remain solely owned by such Party.

10.3  Ownership of Intellectual Property Rights in the Product

All Intellectual Property Rights arising from and during the course of the
Development, including all Intellectual Property Rights:

      10.3.1  to all inventions arising from and during the course of the
              Development;

      10.3.2  to all data, information, know-how and results and the like
              created as part of the Development (the "Data"); and

      10.3.3  relating to the Product or improvements thereto or the process for
              manufacturing the Product;

shall be solely owned by Inex or its designee, regardless of:

      10.3.4  which Party(ies) created or invented the same; and

      10.3.5  whether or not such Intellectual Property Rights are required to
              obtain and maintain Regulatory Approvals;

and shall be licensed to Enzon hereunder as Licensed Patents and Inex Technology
without additional consideration or formality during the Term. Without limiting
the generality of the foregoing, any Elan Improvements made by Enzon, or its
Representatives, regardless of whether or not arising from and during the course
of the Development, shall be solely owned by Elan and sublicensed (within the
Field and within the Territory) without additional consideration to Enzon
through Inex on the terms set out in this Section. Enzon shall cooperate, and
shall cause its Representatives to cooperate, with Inex and Elan, at Elan's
expense, in perfecting Elan's ownership and other proprietary rights in respect
of any Elan Improvements and Enzon hereby assigns same to Elan and shall execute
and deliver, and cause its Representatives to execute and deliver, to Elan any
documents that Elan may reasonably require with respect thereto. If at any time
Elan does not exercise its rights under this Section, such rights may be
exercised by Inex as if Inex were Elan under this Section.

10.4  Ownership of Regulatory Approvals and Regulatory Submissions

Notwithstanding the terms of Section 10.3:

      10.4.1  Inex or its Representatives will own all Regulatory Approvals and
              Regulatory Submissions made as part of the Development in respect
              of the Product in the Territory and all Intellectual Property
              Rights in same; and

      10.4.2  Inex or its Representatives may use all Data and Regulatory
              Approvals and Regulatory Submissions, in Inex or its
              Representative's efforts to register and commercialize the Product
              outside the Territory and inside the Territory but outside the
              Field.

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       32


10.5  Ownership of Intellectual Property Rights Outside the Development

Except as otherwise provided in Sections 10.3 and 10.4, each Party shall have
and retain sole and exclusive title to all inventions, discoveries and know-how
which are made, conceived, reduced to practice or generated by its
Representatives. For greater certainty, Intellectual Property Rights or
inventions or creations generated outside the Development and without access to
the other Party's Confidential Information shall not be licensed hereunder or
included in the Licensed Patents or Inex Technology.

                             Article 11 Termination

11.1  Term

This Agreement shall become effective on the Effective Date and, unless earlier
terminated as provided for herein, shall expire, on a country-by-country basis,
upon the later of:

      11.1.1  expiration of the last to expire of the Licensed Patents
              containing Valid Claims covering the Product in such country in
              the Territory; and

      11.1.2  fifteen years from the date of the First Commercial Sale in that
              country;

and such period shall be the "Term" under this Agreement.

11.2  Renewal

On or before six months before the expiration of this Agreement in accordance
with its terms, Enzon may notify Inex in writing that Enzon wishes to renew this
Agreement. In the event that Enzon so notifies Inex, the Parties will negotiate
in good faith for the extension of the Term. If the Parties have not reached
agreement in writing to extend the Term on or before the expiry of the Term,
this Section 11.2 shall be of no further force or effect.

11.3  Voluntary Termination

      11.3.1  In the event that Enzon does not have a significant interest in
              obtaining or maintaining Regulatory Approval of and marketing
              Product in any country of the Territory, Enzon shall promptly
              notify Inex in writing. If Inex requests in writing that Enzon
              indicate whether or not Enzon has an interest in obtaining or
              maintaining Regulatory Approval of and marketing Product in a
              country(ies) of the Territory, within thirty (30) days thereafter
              Enzon shall notify Inex in writing as to whether or not Enzon has
              such an interest. In the event that:

              (a)       Enzon notifies Inex that it does not have a significant
                        interest in obtaining or maintaining Regulatory Approval
                        of and marketing Product in any country(ies) of the
                        Territory; or

              (b)       Enzon does not respond in writing within thirty (30)
                        days of Enzon's receipt of Inex's query;

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       33


              (c)       Inex may terminate all licenses granted to Enzon
                        pursuant to this Agreement in respect of such
                        country(ies) of the Territory, and such country(ies)
                        shall no longer form part of the Territory.

      11.3.2  Enzon may terminate this Agreement in its entirety at any time by:

              (a)       providing Inex ninety (90) days prior written notice of
                        Enzon's intention to terminate;

              (b)       paying all outstanding obligations due to Inex,
                        including Enzon's portion of all non-cancelable
                        Development Costs incurred by Inex and its Affiliates
                        pursuant to the Related Agreements as of the date of
                        termination; and

              (c)       paying a termination fee of two million dollars
                        ($2,000,000), unless such termination is effected after
                        12 months from the Effective Date but prior to Inex
                        completing its NDA submission to the FDA for the
                        Product.

              (d)       All amounts due hereunder shall be paid by Enzon to Inex
                        within ten (10) days of termination, without reduction,
                        except as agreed in writing between the parties.

11.4  Termination for Breach

Each Party shall be entitled to terminate this Agreement and the licenses
granted hereunder to the other Party by written notice to the other Party in the
event that the other Party shall be in material default of any of its
obligations hereunder, and shall fail to remedy any such default within ninety
(90) days after notice thereof by the non-breaching Party. Any such notice shall
specifically state that the non-breaching Party intends to terminate this
Agreement in the event that the breaching Party shall fail to remedy the
default. Any such notice shall set out expressly the actions required of the
breaching Party to remedy the default. If such default is not corrected, the
non-breaching Party shall have the right to terminate this Agreement by giving
written notice to the Party in default provided the notice of termination is
given within six (6) months of the default and prior to correction of the
default.

11.5  Termination upon Bankruptcy

      11.5.1  This Agreement may be terminated by a Party by providing written
              notice to the other Party upon:

              (a)       the bankruptcy, liquidation or dissolution of the other
                        Party;

              (b)       the filing of any voluntary petition for bankruptcy,
                        dissolution, liquidation or winding-up of the affairs of
                        the other Party; or

              (c)       the filing of any involuntary petition for bankruptcy,
                        dissolution, liquidation or winding-up of the affairs of
                        the other Party which is not dismissed within one
                        hundred twenty (120) days after the date on which it is
                        filed or commenced.

      11.5.2  Notwithstanding the foregoing, either Party may seek the waiver of
              the operation of Section 11.5.1 in advance of any event giving
              rise to a right of termination under Section 11.5.1(b), and,
              provided that:

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       34


              (a)       the requesting Party is in good standing and not in
                        breach of any of the terms of the Related Agreements;

              (b)       the requesting Party is in reasonable financial
                        condition; and

              (c)       the Party whose consent is sought will not be prejudiced
                        by granting such waiver,

              the Party whose consent is sought will not unreasonably withhold
              its consent to such waiver. Such waiver may be revocable in the
              event of a material adverse change in circumstances related to the
              requesting Party not contemplated at the time of granting the
              waiver.

11.6  Survival of Obligations; Return of Confidential Information

      11.6.1  Upon any termination of this Agreement pursuant to this Article
              11, neither Party shall be relieved of any obligations incurred
              prior to such termination.

      11.6.2  Upon any termination of this Agreement pursuant to this Article
              11, the licenses granted in Section 2.1 will forthwith terminate.

      11.6.3  Notwithstanding any termination of this Agreement, the obligations
              of the Parties under Article 1, Sections 5.9 and 5.10, Article 9,
              Article 10, Article 11 and Article 12, as well as under any other
              provisions which by their nature are intended to survive any such
              termination, shall survive and continue to be enforceable. 11.6.4
              Upon any termination of this Agreement pursuant to this Article
              11, except as contemplated hereby, each Party shall promptly
              return to the other Party all written Confidential Information,
              and all copies thereof (except for one archival copy to be
              retained by a person designated by such Party (who shall not make
              such Confidential Information generally available to employees or
              other representatives of such Party) for the purpose of confirming
              which information to hold in confidence hereunder), of the other
              Party which is not covered by a license surviving such
              termination.

11.7  Additional Consequences of Termination

      11.7.1  On or before the effective date of termination of this Agreement,
              except as otherwise set forth herein:

              (a)       Enzon shall promptly deliver to Inex a copy of all Data
                        and such other information, materials (including
                        biological materials) and documents in Enzon's
                        possession or control arising from the development of
                        the Product under this Agreement, including, without
                        limitation, the Development, provided that Inex shall be
                        responsible for any reasonable associated Out-of-Pocket
                        Costs associated with transferring same;

              (b)       Enzon shall pay its share of the Development Costs as
                        determined in accordance with Article 5, including all
                        non-cancelable Development Costs reasonably committed to
                        by Inex and its Affiliates prior to the termination of
                        the Agreement;

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       35


              (c)       in the event that such termination occurs before the
                        payment of all of the milestone payments referred to in
                        Section Error! Reference source not found., then,
                        concurrently with such termination, Enzon shall pay to
                        Inex the next such payment, pro-rated so that such
                        payment is reduced by the proportion of the year
                        remaining prior to the date for such payment as of the
                        effective date of such termination;

              (d)       Enzon's right to use the Data pursuant to Section 10.4.2
                        will forthwith terminate;

              (e)       all licenses and sublicenses granted pursuant to this
                        Agreement shall forthwith terminate;

              (f)       Enzon shall:

                        (i)   use all reasonable endeavors to take all steps and
                              execute all documents reasonably necessary to
                              assign and/or transfer or permit reference to (to
                              the extent legally permissible in the relevant
                              country) all Regulatory Approvals and Regulatory
                              Submissions arising from the development of the
                              Product under this Agreement, including, without
                              limitation, the Development, in Enzon's name or in
                              the name of Enzon's Affiliates or Sublicensees, to
                              Inex or its designee;

                        (ii)  provide to Inex or its designee copies of or
                              access to all correspondence, meeting minutes and
                              any other written information exchanged between
                              Enzon and any Regulatory Authority(ies) regarding
                              such Regulatory Approvals and Regulatory
                              Submissions;

                        (iii) in the event that no such assignment and/or
                              transfer and/or reference pursuant to Section
                              11.7.1(f)(i) may legally be made, then Enzon shall
                              forthwith surrender such Regulatory Approvals and
                              Regulatory Submissions for cancellation; and

                        (iv)  upon Inex's request, Enzon shall within the same
                              period deliver to Inex or its designee any and all
                              documents relating to Regulatory Approvals and
                              Regulatory Submissions in its possession or
                              control arising from the Development that are
                              reasonably required in order to file, obtain or
                              maintain Regulatory Approvals for the Product.

11.8  Termination on a Country by Country Basis

In the event of termination of this Agreement in respect of one or more
country(ies) in the Territory pursuant to Section 11.3.1, then Sections 11.6 and
11.7 shall apply in respect of the country(ies) to which such termination
applies.

11.9  Termination of Related Agreements

In the event of termination of this Agreement, the Related Agreements shall
terminate with immediate effect, subject to any continuing or surviving
obligations as set forth in each such Related Agreement.

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       36


                            Article 12 Miscellaneous

12.1  Assignment

      12.1.1  The rights and obligations set out in this Agreement are personal
              to each Party and for this reason, except as expressly set out in
              this Agreement, this Agreement will not be assignable by either
              Party in whole or in part, nor will either Party subcontract any
              of its obligations hereunder without the prior written consent of
              the other Party, which consent shall not be withheld or delayed
              unreasonably; provided, however, that the restriction contained
              herein will in no way limit the rights of either Party to:

              (a)       assign or subcontract any right or obligation hereunder
                        to any of its Affiliates; or

              (b)       appoint as its agent for any purpose of this Agreement
                        any such Affiliate; or

              (c)       assign any right or obligation hereunder to any person
                        or entity that:

                        (i)   purchases all or substantially all of its assets
                              to which this Agreement relates or

                        (ii)  purchases all or substantially all of the stock of
                              either Party; or

                        (iii) acquires or is combined with either Party in a
                              merger or some other form of business combination.

      12.1.2  This Agreement will be binding upon and will enure to the benefit
              of the parties hereto and to any permitted assignee or successor
              of either party.

      12.1.3  Subject to other provisions of this Section 12.1, if one Party
              validly assigns or subcontracts any or all of its obligations
              hereunder, such assigning or subcontracting Party agrees to remain
              bound by all of its responsibilities and obligations hereunder.

      12.1.4  Any and all assignments of this Agreement or any interest herein
              not made in accordance with this Section 12.1 will be void ab
              initio.

12.2  Counterparts

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

12.3  Force Majeure

In the event that either Party is prevented from performing or is unable to
perform any of its obligations under this Agreement due to any act of God; fire;
casualty; flood; war; strike; lockout; failure of public utilities; injunction
or any act, exercise, assertion or requirement of governmental authority;
epidemic; destruction of production facilities; riots; insurrection; failure of
transportation; inability to procure or use materials; or any other cause beyond
the reasonable control of the Party invoking this Section 12.3 if such Party
shall have used its reasonable efforts to avoid such occurrence, such Party
shall give notice to the other Party in writing promptly, and thereupon the
affected Party's performance shall be excused and the

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       37


time for performance shall be extended for the period of delay or inability to
perform due to such occurrence.

12.4  Further Assurances

Each Party hereto agrees to execute, acknowledge and deliver such further
instruments and do all such further acts as may be necessary or appropriate to
carry out the purposes and intent of this Agreement.

12.5  International Sale of Goods Act

The Parties acknowledge and agree that the International Sale of Goods Act and
the United Nations Convention on Contracts for the International Sale of Goods
have no application to this Agreement.

12.6  Modification

No waiver, alteration or modification of any of the provisions hereof shall be
binding unless made in writing and signed by the Parties by their respective
officers thereunto duly authorized.

12.7  No Agency

Nothing herein shall be deemed to constitute either Party as the agent or
Representative of the other Party, or both Parties as joint venturers or
partners for any purpose. Inex shall be an independent contractor, not an
employee or partner of Enzon, and the manner in which Inex renders its services
under this Agreement shall be within Inex's sole discretion. Neither Party shall
be responsible for the acts or omissions of the other Party, and neither Party
will have authority to speak for, represent or obligate the other Party in any
way without prior written authority from the other Party.

12.8  No Solicitation or Hiring of Employees

During the Development and for one year thereafter, neither Inex nor Enzon
shall, without the prior consent of the other Party, solicit the employment of
or hire any person who during the course of employment with the other Party was
involved with activities under the Development Plan and who when solicited or to
be hired is a current employee of the other Party.

12.9  Non-Use of Names

Except as otherwise expressly set out in this Agreement, neither Party shall use
the name of the other Party, nor any adaptation thereof, in any advertising,
promotional or sales literature without prior written consent obtained from such
other Party in each case (which consent shall not be unreasonably withheld or
delayed).

12.10 Notices

Any notice or other communication in connection with this Agreement must be in
writing and if by mail, by registered mail, return receipt requested, and shall
be effective when delivered to the addressee at the address listed below or such
other address as the addressee shall have specified in a notice actually
received by the addressor.

If to Inex:

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       38


         Inex Pharmaceuticals, Inc.
         c/o Corporation Trust Center
         1209 Orange Street
         Wilmington, DE 19801

         Attention: President and CEO

         With copies to:

         Inex Pharmaceuticals Corporation
         100-8900 Glenlyon Parkway
         Burnaby, British Columbia
         Canada V5J 5J8
         Fax: 604-419-3202
         Attention: Sr. V.P. Commercial Operations, and

         With a copy to:

         Inex Pharmaceuticals Corporation
         100-8900 Glenlyon Parkway
         Burnaby, British Columbia
         Canada V5J 5J8
         Fax: 604-419-3202
         Attention: Business Development

         and: Lang Michener
         1500-1055 West Georgia Street
         Vancouver, British Columbia
         Canada V5J 5J8
         Fax: 604-685-7084
         Canada V6E 4N7

         Attention: Leo Raffin

         and:

         Farris, Vaughan, Wills & Murphy
         2600 - 700 West Georgia Street
         Vancouver, British Columbia
         Canada V7Y 1B3
         Fax: 604-661-9349
         Attention: James Hatton

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       39


      If to Enzon:

      Enzon Pharmaceuticals, Inc.
      685 Route 202/206
      Bridgewater, New Jersey, USA 08807
      Fax: 908.541.8680
      Attention: V.P. Business Development

      with a copy to:

      Enzon Pharmaceuticals, Inc.
      685 Route 202/206
      Bridgewater, NJ 08807
      Attention: General Counsel
      Fax: 908.541.8838

12.11 Publicity

Except as required by law, stock exchange or Regulatory Authority:

      12.11.1 neither Party, nor any of its Affiliates, shall originate any
              publicity, news release or other public announcement, written or
              oral, relating to this Agreement or the existence of an
              arrangement between the Parties, without the prior written
              approval of the other Party and agreement upon the nature and text
              of such announcement or disclosure, which approval shall not be
              unreasonably withheld;

      12.11.2 the Party desiring to make any such public announcement or other
              disclosure shall inform the other Party of the proposed
              announcement or disclosure in reasonably sufficient time prior to
              public release, and shall provide the other Party with a written
              copy thereof, in order to allow such other Party to comment upon
              such announcement or disclosure; and

      12.11.3 notwithstanding the foregoing, the Parties agree that the press
              release set out as an Exhibit to the Product Supply Agreement
              shall be released by the Parties upon execution and delivery of
              this Agreement by both Parties.

12.12 No Third Party Beneficiaries

Except as expressly set out in this Agreement, nothing in this Agreement is
intended to or shall confer upon any Third Part any legal or equitable right,
benefit or remedy of any nature whatsoever.

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       40


12.13 Waiver

The waiver by either Party of a breach or a default of any provision of this
Agreement by the other Party shall not be construed as a waiver of any
succeeding breach of the same or any other provision, nor shall any delay or
omission on the part of either Party to exercise or avail itself of any right,
power or privilege that it has or may have hereunder operate as a waiver of any
right, power or privilege by such Party.

12.14 Cross Default

A breach of or default under any of the Related Agreements other than the
Co-Promotion Agreement shall constitute a breach of and default under all the
Related Agreements.

IN WITNESS WHEREOF, the Parties hereto have caused this Development Agreement to
be executed as a sealed instrument in their names by their properly and duly
authorized officers or representatives.

Inex Pharmaceuticals, Inc.

By: /s/ David J. Main
    ---------------------------
Name:  David J. Main
Title: President & CEO


Enzon Pharmaceuticals, Inc.

By: /s/ Arthur J. Higgins
    ---------------------------
Name:  Arthur J. Higgins
Title: Chairman & CEO

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       41


Exhibit 1.1.1: Adverse Drug Event

                             ADVERSE DRUG EVENT FORM

      An Adverse Drug Event shall mean any noxious, unintended, or untoward
      medical occurrence in a patient or clinical investigation subject
      associated with the use of a medicinal or investigational product, whether
      or not related to the medicinal or investigational product.

      This Form must be completed and faxed to the Regulatory Authorities (with
      a copy provided to the other Party)::

a)    Immediately, or not later than 24 hours following receipt of any
      information relating to an Adverse Drug Event; and

b)    No later than two (2) business days following receipt of any information
      relating to a product complaint.

      Complaint Date:__________________________

      Complaint received by:___________________  Title:________________________

      Manner complaint received in:    Oral |_|       Written |_|     Faxed |_|
                                       Other:_________________

      Complainant's name:__________________ Phone:___________ Fax: _____________

      Clinic's name:_________________ Phone:_____________ Fax:__________________

      Clinic's Address:_________________________________________________________

      Product Name: ___________ Lot number: ___________ Expiry Date: ___________

      Description of Product Complaint or Adverse Drug Event:___________________

      __________________________________________________________________________

      __________________________________________________________________________

      __________________________________________________________________________

      __________________________________________________________________________

      __________________________________________________________________________

      __________________________________________________________________________

      __________________________________________________________________________

      __________________________________________________________________________

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       42


Exhibit 1.1.27: ***


*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       43


Exhibit 1.1.36: ***

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       44


Exhibit 5.2.1(c): Ongoing Phase II Clinical Trials

***

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.

<PAGE>
                                       45


Exhibit 6.1: Joint Steering Committee Responsibilities

The members of the Joint Steering Committee as of the Effective Date are:

For Enzon:

      Eddy Anglade, VP - Clinical

      Clarke Atwell, VP - Sales & Marketing

      Katherine Bishburg, VP - Regulatory

      Eric Liebler, VP - Business Development

For Inex:

      Tom MacRury, Senior VP, Commercial Opoerations

      Alexandra Mancini, Senior VP, Clinical and Regulatory Affairs

      Jeff Charpentier, VP Finance and CFO

      Linda Diano, Director, Project Management

The Joint Steering Committee shall have responsibilities including:

1.    review amendments to the Development Plan and submit same to the Parties
      for review and approval;

2.    establish working committees to conduct work under the Development Plan;

3.    assign responsibility for conducting all needed Development work
      appropriately between the Parties, including providing for subcontractors
      to perform certain tasks if desirable;

4.    oversee all Development activities, including the review and approval as
      appropriate, of all reports on the progress of Development;

5.    coordinate the overall strategy for Development and commercialization;

6.    meet quarterly, circulate agendas at least one (1) week in advance of each
      quarterly meeting, and circulate minutes of meetings within two (2) weeks
      following each meeting;

7.    verify the reports of Development Costs;

8.    such other duties and responsibilities as may be agreed upon by the
      Parties; and

9.    be the primary contact point between the Parties regarding the transfer of
      information and the discussion of each Party's efforts to conduct
      Development.

*** Indicates the omission of confidential material pursuant to a request for
confidential treatment made in accordance with Rule 24b-2 under the Securities
Exchange Act of 1934, as amended. The Confidential material is being filed
separately with the Secretary to the Securities and Exchange Commission.