Document:

Exhibit 10.23

                                   ENZON, INC.
                          2001 INCENTIVE STOCK PLAN(1)

Section 1. Purpose

      The purpose of the Plan is to promote the interests of the Company and its
shareholders by aiding the Company in attracting and retaining employees,
officers, consultants, independent contractors and Non-Employee Directors
capable of contributing to the future success of the Company, to offer such
persons incentives to put forth maximum efforts for the success of the Company's
business and to afford such persons an opportunity to acquire a proprietary
interest in the Company.

Section 2. Definitions

As used in the Plan, the following terms shall have the meanings set forth
below:

      "Affiliate" shall mean (i) any entity that, directly or indirectly through
      one or more intermediaries, is controlled by the Company and (ii) any
      entity in which the Company has a significant equity interest, in each
      case as determined by the Committee.

      "Award" shall mean any Option, Stock Appreciation Right, Restricted Stock,
      Restricted Stock Unit, Performance Award, Dividend Equivalent, Other Stock
      Grant or Other Stock-Based Award granted under the Plan.

      "Award Agreement" shall mean any written agreement, contract or other
      instrument or document evidencing any Award granted under the Plan. Each
      Award Agreement shall be subject to the applicable terms and conditions of
      the Plan and any other terms and conditions (not inconsistent with the
      Plan) determined by the Committee.

      "Board" shall mean the Board of Directors of the Company.

      "Code" shall mean the Internal Revenue Code of 1986, as amended from time
      to time, and any regulations promulgated thereunder.

      "Committee" shall mean a committee of Directors designated by the Board to
      administer the Plan. The Committee shall be comprised of not less than
      such number of Directors as shall be required to permit Awards granted
      under the Plan by the Committee to qualify under Rule 16b-3, and each
      member of the Committee shall be a "Non-Employee Director" within the
      meaning of Rule 16b-3 and an "outside director" within the meaning of
      Section 162(m) of the Code. The Company expects to have the Plan
      administered in accordance with the requirements for the award of
      "qualified performance-based compensation" within the meaning of Section
      162(m) of the Code.

      "Company" shall mean Enzon, Inc., a Delaware corporation, and any
      successor corporation.

      "Director" shall mean a member of the Board, including Non-Employee
      Directors.

      "Dividend Equivalent" shall mean any right granted under Section 6(E) of
      the Plan.

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(1)   As amended on November 12, 2003 and December 2, 2003.

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      "Eligible Person" shall mean any employee, officer, consultant,
      independent contractor or Director (including any Non-Employee Director)
      providing services to the Company or any Affiliate whom the Committee
      determines to be an Eligible Person.

      "Exchange Act" shall mean the Securities Exchange Act of 1934, as amended.

      "Fair Market Value" shall mean, with respect to any property (including,
      without limitation, any Shares or other securities), the fair market value
      of such property determined by such methods or procedures as shall be
      established from time to time by the Committee. Notwithstanding the
      foregoing, unless otherwise determined by the Committee, the Fair Market
      Value of a Share as of a given date shall be, if the Shares are then
      traded on the Nasdaq National Market, the last reported sale price of one
      Share as reported on the Nasdaq National Market on such date or, if the
      Nasdaq National Market is not open for trading on such date, on the most
      recent preceding date when it is open for trading.

      "Family Members" shall be those persons related to a Participant as
      determined by the Committee.

      "Incentive Stock Option" shall mean an option granted under Section 6A of
      the Plan that is intended to meet the requirements of Section 422 of the
      Code or any successor provision.

      "Non-Employee Director" shall have the meaning ascribed in Rule 16b-3
      promulgated under the Exchange Act or any successor provision.

      "Non-Qualified Stock Option" shall mean an option granted under Section 6A
      of the Plan that is not intended to be an Incentive Stock Option.

      "Option" shall mean an Incentive Stock Option or a Non-Qualified Stock
      Option.

      "Other Stock Grant" shall mean any right granted under Section 6F of the
      Plan.

      "Other Stock-Based Award" shall mean any right granted under Section 6G of
      the Plan.

      "Participant" shall mean an Eligible Person designated to be granted an
      Award under the Plan.

      "Performance Award" shall mean any right granted under Section 6D of the
      Plan.

      "Person" shall mean any individual, corporation, partnership, association
      or trust.

      "Plan" shall mean the Enzon, Inc. 2001 Incentive Stock Plan, as amended
      from time to time, the provisions of which are set forth herein.

      "Plan Year" shall mean a consecutive 12-month period ending on December 31
      of each year.

      "Reload Option" shall mean any Option granted under Section 6A(5) of the
      Plan.

      "Restricted Stock" shall mean any Shares granted under Section 6C of the
      Plan.

      "Restricted Stock Unit" shall mean any unit granted under Section 6C of
      the Plan evidencing the right to receive a Share (or a cash payment equal
      to the Fair Market Value of a Share) at some future date.

      "Rule 16b-3" shall mean Rule 16b-3 promulgated by the Securities and
      Exchange Commission under the Exchange Act, or any successor rule or
      regulation.

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      "Share" or "Shares" shall mean shares of common stock, $0.01 par value per
      share, of the Company or such other securities or property as may become
      subject to Awards pursuant to an adjustment made under Section 4C of the
      Plan.

      "Stock Appreciation Right" shall mean any right granted under Section 6B
      of the Plan.

Section 3. Administration

      Power and Authority of the Committee. The Plan shall be administered by
the Committee. Subject to the express provisions of the Plan and to applicable
law, the Committee shall have full power and authority to: (i) designate
Participants; (ii) determine the type or types of Awards to be granted to each
Participant under the Plan; (iii) determine the number of Shares to be covered
by (or the method by which payments, or other rights are to be calculated in
connection with) each Award; (iv) determine the terms and conditions of any
Award or Award Agreement; (v) amend the terms and conditions of any Award or
Award Agreement and accelerate the exercisability of any Award or the lapse of
restrictions relating to any Award; (vi) determine whether, to what extent and
under what circumstances Awards may be exercised in cash, Shares, promissory
notes, other securities, other Awards or other property, or canceled, forfeited
or suspended; (vii) determine whether, to what extent and under what
circumstances cash, Shares, promissory notes, other securities, other Awards,
other property and other amounts payable with respect to an Award under the Plan
shall be deferred either automatically or at the election of the holder thereof
or the Committee; (viii) interpret and administer the Plan and any instrument or
agreement, including an Award Agreement, relating to the Plan; (ix) establish,
amend, suspend or waive such rules and regulations and appoint such agents as it
shall deem appropriate for the proper administration of the Plan; and (x) make
any other determination and take any other action that the Committee deems
necessary or desirable for the administration of the Plan. Unless otherwise
expressly provided in the Plan, all designations, determinations,
interpretations and other decisions under or with respect to the Plan or any
Award shall be within the sole discretion of the Committee, may be made at any
time and shall be final, conclusive and binding upon any Participant, any holder
or beneficiary of any Award and any employee of the Company or any Affiliate.

      Delegation. The Committee may delegate its powers and duties under the
Plan to one or more Directors or officers of the Company, or to a committee of
Directors or officers, subject to such terms, conditions and limitations as the
Committee may establish in its sole discretion, provided, however, that the
Committee shall not delegate its powers and duties under the Plan (i) with
regard to officers or directors of the Company or any Affiliate who are subject
to Section 16 of the Exchange Act or (ii) in such a manner as would cause the
Plan not to comply with the requirements of Section 162(m) of the Code.

      Power and Authority of the Board. Notwithstanding anything to the contrary
contained herein, the Board may, at any time and from time to time, without any
further action of the Committee, exercise the powers and duties of the Committee
under the Plan.

Section 4. Shares Available for Awards

      A. Shares Available. Subject to adjustment as provided in Section 4C of
the Plan, the aggregate number of Shares that may be issued under all Awards
under the Plan shall be 6,000,000(2); provided that, any Shares with respect to
which Awards may be issued, but are not issued, under the Plan in any Plan Year
shall be carried forward and shall be available to be covered by Awards issued
in any subsequent Plan Year in which Awards may be issued under the Plan. Shares
to be issued under the Plan may be either authorized but unissued Shares or
Shares acquired in the open market or otherwise. Any Shares that are used by a
Participant as full or partial payment to the Company of the purchase price
relating to an Award, or in connection with the satisfaction of tax obligations
relating to an Award, shall again be available for granting Awards (other than
Incentive Stock Options) under the Plan. In addition, if any Shares covered by
an Award or to which an Award relates are not purchased or are forfeited, or if
an Award otherwise terminates without delivery of any Shares, then the number of
Shares counted

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(2)   Increased from 2,000,000 to 6,000,000 pursuant resolutions adopted by the
      stockholders on December 2, 2003.

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against the aggregate number of Shares available under the Plan with respect to
such Award, to the extent of any such forfeiture or termination, shall again be
available for granting Awards under the Plan. Notwithstanding the foregoing, the
number of Shares available for granting Incentive Stock Options under the Plan
shall not exceed 2,000,000 shares subject to adjustment as provided in the Plan
and subject to the provisions of Section 422 or 424 of the Code or any successor
provision.

      B. Accounting for Awards. For purposes of this Section 4, if an Award
entitles the holder thereof to receive or purchase Shares, the number of Shares
covered by such Award or to which such Award relates shall be counted on the
date of grant of such Award against the aggregate number of Shares available for
granting Awards under the Plan.

      C. Adjustments. In the event that the Committee shall determine that any
dividend or other distribution (whether in the form of cash, Shares, other
securities or other property), recapitalization, stock split, reverse stock
split, reorganization, merger, consolidation, split-up, spin-off, combination,
issuance of warrants or other rights to purchase Shares or other securities of
the Company to all holders of common stock pro rata whether as a dividend or
otherwise or other similar corporate transaction or event affects the Shares
such that an adjustment is determined by the Committee to be appropriate in
order to prevent dilution or enlargement of the benefits or potential benefits
intended to be made available under the Plan, then the Committee shall, in such
manner as it may deem equitable, adjust any or all of (i) the number and type of
Shares (or other securities or other property) that thereafter may be made the
subject of Awards, (ii) the number and type of Shares (or other securities or
other property) subject to outstanding Awards and (iii) the purchase or exercise
price with respect to any Award; provided, however, that the number of Shares
covered by any Award or to which such Award relates shall always be a whole
number.

      D. Award Limitations Under the Plan. No Eligible Person may be granted any
Award or Awards under the Plan, the value of which Award or Awards is based
solely on an increase in the value of the Shares after the date of grant of such
Award or Awards, for more than 1,000,000 Shares (subject to adjustment as
provided for in Section 4(c) of the Plan), in the aggregate in any calendar
year. The foregoing annual limitation specifically includes the grant of any
Award or Awards representing "qualified performance-based compensation" within
the meaning of Section 162(m) of the Code.

Section 5. Eligibility.

      Any Eligible Person shall be eligible to be designated a Participant. In
determining which Eligible Persons shall receive an Award and the terms of any
Award, the Committee may take into account the nature of the services rendered
by the respective Eligible Persons, their present and potential contributions to
the success of the Company or such other factors as the Committee, in its
discretion, shall deem relevant. Notwithstanding the foregoing, an Incentive
Stock Option may only be granted to full or part-time employees (which term as
used herein includes, without limitation, officers and Directors who are also
employees), and an Incentive Stock Option shall not be granted to an employee of
an Affiliate unless such Affiliate is also a "subsidiary corporation" of the
Company within the meaning of Section 424(f) of the Code or any successor
provision.

Section 6. Awards

      A.    Options. The Committee is hereby authorized to grant Options to
            Eligible Persons with the following terms and conditions and with
            such additional terms and conditions not inconsistent with the
            provisions of the Plan as the Committee shall determine:

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            1.    Exercise Price. The purchase price per Share purchasable under
                  an Option shall be determined by the Committee; provided,
                  however, that such purchase price shall not be less than 100%
                  of the Fair Market Value of a Share on the date of grant of
                  such Option.

            2.    Option Term. The term of each Option shall be fixed by the
                  Committee, but, shall in no event exceed 10 years from the
                  date on which such Option is granted.

            3.    Time and Method of Exercise. The Committee shall determine the
                  time or times at which an Option may be exercised in whole or
                  in part and the method or methods by which, and the form or
                  forms (including, without limitation, cash, Shares, promissory
                  notes, other securities, other Awards or other property, or
                  any combination thereof, having a Fair Market Value on the
                  exercise date equal to the applicable exercise price) in
                  which, payment of the exercise price with respect thereto may
                  be made or deemed to have been made.

            4.    Incentive Stock Options. Notwithstanding anything in the Plan
                  to the contrary, the following additional provisions shall
                  apply to the grant of stock options which are intended to
                  qualify as Incentive Stock Options:

                        (a) The aggregate Fair Market Value (determined as of
                        the time the option is granted) of the Shares with
                        respect to which Incentive Stock Options are exercisable
                        for the first time by any Participant during any
                        calendar year (under this Plan and all other plans of
                        the Company and its Affiliates) shall not exceed
                        $100,000.

                        (b) All Incentive Stock Options must be granted within
                        ten years from the earlier of the date on which this
                        Plan was adopted by the Board or the date this Plan was
                        approved by the shareholders of the Company.

                        (c) Unless sooner exercised, all Incentive Stock Options
                        shall expire and no longer be exercisable no later than
                        10 years after the date of grant; provided, however,
                        that in the case of a grant of an Incentive Stock Option
                        to a Participant who, at the time such Option is
                        granted, owns (within the meaning of Section 422 of the
                        Code) stock possessing more than 10% of the total
                        combined voting power of all classes of stock of the
                        Company or of its Affiliate, such Incentive Stock Option
                        shall expire and no longer be exercisable no later than
                        5 years from the date of grant.

                        (d) The purchase price per Share for an Incentive Stock
                        Option shall be not less than 100% of the Fair Market
                        Value of a Share on the date of grant of the Incentive
                        Stock Option; provided, however, that, in the case of
                        the grant of an Incentive Stock Option to a Participant
                        who, at the time such Option is granted, owns (within
                        the meaning of Section 422 of the Code) stock possessing
                        more than 10% of the total combined voting power of all
                        classes of stock of the Company or of its Affiliate, the
                        purchase price per Share purchasable under an Incentive
                        Stock Option shall be not less than 110% of the Fair
                        Market Value of a Share on the date of grant of the
                        Inventive Stock Option.

                        (e) Any Incentive Stock Option authorized under the Plan
                        shall contain such other provisions as the Committee
                        shall deem advisable, but shall in all events be
                        consistent with and contain all provisions required in
                        order to qualify the Option as an Incentive Stock
                        Option.

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            5.    Reload Options. The Committee may grant Reload Options,
                  separately or together with another Option, pursuant to which,
                  subject to the terms and conditions established by the
                  Committee, the Participant would be granted a new Option when
                  the payment of the exercise price of a previously granted
                  option is made by the delivery of Shares owned by the
                  Participant pursuant to Section 6A(3) hereof or the relevant
                  provisions of another plan of the Company, and/or when Shares
                  are tendered or withheld as payment of the amount to be
                  withheld under applicable income tax laws in connection with
                  the exercise of an Option, which new Option would be an Option
                  to purchase the number of Shares not exceeding the sum of (A)
                  the number of Shares so provided as consideration upon the
                  exercise of the previously granted option to which such Reload
                  Option relates and (B) the number of Shares, if any, tendered
                  or withheld as payment of the amount to be withheld under
                  applicable tax laws in connection with the exercise of the
                  option to which such Reload Option relates pursuant to the
                  relevant provisions of the plan or agreement relating to such
                  option. Reload Options may be granted with respect to Options
                  previously granted under the Plan or any other stock option
                  plan of the Company or may be granted in connection with any
                  Option granted under the Plan or any other stock option plan
                  of the Company at the time of such grant. Such Reload Options
                  shall have a per share exercise price equal to the Fair Market
                  Value of one Share as of the date of grant of the new Option.
                  Any Reload Option shall be subject to availability of
                  sufficient Shares for grant under the Plan. Shares surrendered
                  as part or all of the exercise price of the Option to which it
                  relates that have been owned by the optionee less than six
                  months will not be counted for purposes of determining the
                  number of Shares that may be purchased pursuant to a Reload
                  Option.

B. Stock Appreciation Rights. The Committee is hereby authorized to grant Stock
Appreciation Rights to Eligible Persons subject to the terms of the Plan and any
applicable Award Agreement. A Stock Appreciation Right granted under the Plan
shall confer on the holder thereof a right to receive upon exercise thereof the
excess of (i) the Fair Market Value of one Share on the date of exercise (or, if
the Committee shall so determine, at any time during a specified period before
or after the date of exercise) over (ii) the grant price of the Stock
Appreciation Right as specified by the Committee, which price shall not be less
than 100% of the Fair Market Value of one Share on the date of grant of the
Stock Appreciation Right. Subject to the terms of the Plan and any applicable
Award Agreement, the grant price, term, methods of exercise, dates of exercise,
methods of settlement and any other terms and conditions of any Stock
Appreciation Right shall be as determined by the Committee. The Committee may
impose such conditions or restrictions on the exercise of any Stock Appreciation
Right as it may deem appropriate.

C. Restricted Stock and Restricted Stock Units. The Committee is hereby
authorized to grant Restricted Stock and Restricted Stock Units to Eligible
Persons with the following terms and conditions and with such additional terms
and conditions not inconsistent with the provisions of the Plan as the Committee
shall determine:

      1.    Restrictions. Shares of Restricted Stock and Restricted Stock Units
            shall be subject to such restrictions as the Committee may impose
            (including, without limitation, a waiver by the Participant of the
            right to vote or to receive any dividend or other right or property
            with respect thereto), which restrictions may lapse separately or in
            combination at such time or times, in such installments or otherwise
            as the Committee may deem appropriate.

      2.    Stock Certificates. Any Restricted Stock granted under the Plan
            shall be registered in the name of the Participant and shall bear an
            appropriate legend referring to the terms, conditions and
            restrictions applicable to such Restricted Stock.

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      3.    Forfeiture. Except as otherwise determined by the Committee, upon a
            Participant's termination of employment (as determined under
            criteria established by the Committee) during the applicable
            restriction period, all Shares of Restricted Stock and Restricted
            Stock Units held by the Participant at such time shall be forfeited
            and reacquired by the Company; provided, however, that the Committee
            may, when it finds that a waiver would be in the best interest of
            the Company, waive in whole or in part any or all remaining
            restrictions with respect to Shares of Restricted Stock or
            Restricted Stock Units.

      4.    Aggregate Limit. The maximum number of shares of Restricted Stock
            and Restricted Stock Units that the Committee may grant under the
            Plan shall not exceed 50% of the total number of shares issuable
            pursuant to all Awards under the Plan.(3)

D. Performance Awards. The Committee is hereby authorized to grant Performance
Awards to Eligible Persons subject to the terms of the Plan and any applicable
Award Agreement. A Performance Award granted under the Plan (i) may be
denominated or payable in cash, Shares (including, without limitation,
Restricted Stock and Restricted Stock Units), other securities, other Awards or
other property and (ii) shall confer on the holder thereof the right to receive
payments, in whole or in part, upon the achievement of such performance goals
during such performance periods as the Committee shall establish. Subject to the
terms of the Plan and any applicable Award Agreement, the performance goals to
be achieved during any performance period, the length of any performance period,
the amount of any Performance Award granted, the amount of any payment or
transfer to be made pursuant to any Performance Award and any other terms and
conditions of any Performance Award shall be determined by the Committee.

E. Dividend Equivalents. The Committee is hereby authorized to grant Dividend
Equivalents to Eligible Persons under which the Participant shall be entitled to
receive payments (in cash, Shares, other securities, other Awards or other
property as determined in the discretion of the Committee) equivalent to the
amount of cash dividends paid by the Company to holders of Shares with respect
to a number of Shares determined by the Committee. Subject to the terms of the
Plan and any applicable Award Agreement, such Dividend Equivalents may have such
terms and conditions as the Committee shall determine.

F. Other Stock Grants. The Committee is hereby authorized, subject to the terms
of the Plan and any applicable Award Agreements, to grant to Eligible Persons
Shares without restrictions thereon as are deemed by the Committee to be
consistent with the purpose of the Plan.

G. Other Stock-Based Awards. The Committee is hereby authorized to grant to
Eligible Persons, subject to the terms of the Plan and any applicable Award
Agreements, such other Awards that are denominated or payable in, valued in
whole or in part by reference to, or otherwise based on or related to, Shares
(including, without limitation, securities convertible into Shares), as are
deemed by the Committee to be consistent with the purpose of the Plan. Shares or
other securities delivered pursuant to a purchase right granted under this
Section 6(G) shall be purchased for such consideration, which may be paid by
such method or methods and in such form or forms (including, without limitation,
cash, Shares, promissory notes, other securities, other Awards or other property
or any combination thereof), as the Committee shall determine, the value of
which consideration, as established by the Committee, shall not be less than
100% of the Fair Market Value of such Shares or other securities as of the date
such purchase right is granted.

H. General

      1.    Consideration for Awards. Awards shall be granted for no cash
            consideration or for any cash or other consideration as may be
            determined by the Committee or required by applicable law.

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(3)   Section 6.C.4 inserted pursuant resolutions adopted by the stockholders on
      December 2, 2003.

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      2.    Awards May Be Granted Separately or Together. Awards may, in the
            discretion of the Committee, be granted either alone or in addition
            to, in tandem with or in substitution, for any other Award or any
            award granted under any plan of the Company or any Affiliate other
            than the Plan. Awards granted in addition to or in tandem with other
            Awards or in addition to or in tandem with awards granted under any
            such other plan of the Company or any Affiliate may be granted
            either at the same time as or at a different time from the grant of
            such other Awards or awards.

      3.    Forms of Payment under Awards. Subject to the terms of the Plan and
            of any applicable Award Agreement, payments or transfers to be made
            by the Company or an Affiliate upon the grant, exercise or payment
            of an Award may be made in such form or forms as the Committee shall
            determine (including, without limitation, cash, Shares, promissory
            notes, other securities, other Awards or other property or any
            combination thereof), and may be made in a single payment or
            transfer, in installments or on a deferred basis, in each case in
            accordance with rules and procedures established by the Committee.
            Such rules and procedures may include, without limitation,
            provisions for the payment or crediting of reasonable interest on
            installment or deferred payments or the grant or crediting of
            Dividend Equivalents with respect to installment or deferred
            payments.

      4.    Limits on Transfer of Awards. No Award (other than Other Stock
            Grants) and no right under any such Award shall be transferable by a
            Participant otherwise than by will or by the laws of descent and
            distribution and the Company shall not be required to recognize any
            attempted assignment of such rights by any Participant; provided,
            however, that, if so determined by the Committee, a Participant may,
            in the manner established by the Committee, (a) designate a
            beneficiary or beneficiaries to exercise the rights of the
            Participant and receive any property distributable with respect to
            any Award upon the death of the Participant and (b) transfer Awards,
            except in the case of an Incentive Stock Option, to Family Members
            pursuant to terms determined by the Committee. Except as otherwise
            provided in this Plan or in any applicable Award Agreement or
            amendment thereto (other than an Award Agreement relating to an
            Incentive Stock Option), pursuant to terms determined by the
            Committee, each Award or right under any Award shall be exercisable
            during the Participant's lifetime only by the Participant or, if
            permissible under applicable law, by the Participant's guardian or
            legal representative. Except as otherwise provided in this Plan or
            in any applicable Award Agreement or amendment thereto (other than
            an Award Agreement relating to an Incentive Stock Option), no Award
            or right under any such Award may be pledged, alienated, attached or
            otherwise encumbered, and any purported pledge, alienation,
            attachment or encumbrance thereof shall be void and unenforceable
            against the Company or any Affiliate.

      5.    Term of Awards. The term of each Award shall be for such period as
            may be determined by the Committee; provided, however, that in the
            case of an Incentive Stock Option such Option shall not be
            exercisable after the expiration of 10 years from the date such
            Option is granted.

      6.    Restrictions; Securities Exchange Listing. All Shares or other
            securities delivered under the Plan pursuant to any Award or the
            exercise thereof shall be subject to such restrictions as the
            Committee may deem advisable under the Plan, applicable federal or
            state securities laws and regulatory requirements, and the Committee
            may cause appropriate entries to be made or legends to be placed on
            the certificates for such Shares or other securities to reflect such
            restrictions. If the Shares or other securities of the Company are
            traded on a securities exchange, the Company shall not be required
            to deliver any Shares or other securities covered by an Award unless
            and until such Shares or other securities have been admitted for
            trading on such securities exchange.

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Section 7. Amendment and Termination; Adjustments

      A. Amendments to the Plan. The Board may amend, alter, suspend,
discontinue or terminate the Plan at any time; provided, however, that,
notwithstanding any other provision of the Plan or any Award Agreement, without
the approval of the shareholders of the Company, no such amendment, alteration,
suspension, discontinuation or termination shall be made that, absent such
approval would violate the rules or regulations of the Nasdaq National Market or
any other securities exchange that is applicable to the Company.

      B. Amendments to Awards. The Committee may waive any conditions of or
rights of the Company under any outstanding Award, prospectively or
retroactively. Except as otherwise provided herein or in an Award Agreement, the
Committee may not amend, alter, suspend, discontinue or terminate any
outstanding Award, prospectively or retroactively, if such action would
adversely affect the rights of the holder of such Award, without the consent of
the Participant or holder or beneficiary thereof. Notwithstanding the foregoing,
without the prior approval of Enzon's stockholders, options issued under this
Plan will not be repriced, replaced, or regranted through cancellation, or by
lowering the option exercise price of a previously granted Award.(4)

      C. Correction of Defects, Omissions and Inconsistencies. The Committee may
correct any defect, supply any omission or reconcile any inconsistency in the
Plan or any Award in the manner and to the extent it shall deem desirable to
carry the Plan into effect.

Section 8. Income Tax Withholding

      In order to comply with all applicable national, federal, state or local
income tax laws or regulations, the Company may take such action as it deems
appropriate to ensure that all applicable national, federal, state or local
payroll, withholding, income or other taxes, which are the sole and absolute
responsibility of a Participant, are withheld or collected from such
Participant. In order to assist a Participant in paying all or a portion of the
national, federal, state and local taxes to be withheld or collected upon
exercise or receipt of (or the lapse of restrictions relating to) an Award, the
Committee, in its discretion and subject to such additional terms and conditions
as it may adopt, may permit the Participant to satisfy such tax obligation by
(i) electing to have the Company withhold a portion of the Shares otherwise to
be delivered upon exercise or receipt of (or the lapse of restrictions relating
to) such Award with a Fair Market Value equal to the amount of such taxes or
(ii) delivering to the Company Shares other than Shares issuable upon exercise
or receipt of (or the lapse of restrictions relating to) such Award with a Fair
Market Value equal to the amount of such taxes. The election, if any, must be
made on or before the date that the amount of tax to be withheld is determined.

Section 9. General Provisions

      A. No Rights to Awards. No Eligible Person, Participant or other Person
shall have any claim to be granted any Award under the Plan, and there is no
obligation for uniformity of treatment of Eligible Persons, Participants or
holders or beneficiaries of Awards under the Plan. The terms and conditions of
Awards need not be the same with respect to any Participant or with respect to
different Participants.

      B. Plan Provisions Control. In the event that any provision of an Award
Agreement conflicts with or is inconsistent in any respect with the terms of the
Plan as set forth herein or subsequently amended, the terms of the Plan shall
control.

      C. No Rights of Shareholders. Except with respect to Shares of Restricted
Stock as to which the Participant has been granted the right to vote, neither a
Participant nor the Participant's legal representative shall be, or have any of
the rights and privileges of, a stockholder of the Company with respect to any
Shares issuable to such Participant upon the exercise or payment of any Award,
in whole or in part, unless and until such Shares have been issued in the name
of such Participant or such Participant's legal representative without
restrictions thereto.

----------
(4)   Last sentence of Section 7.B added pursuant to resolutions adopted by the
      Compensation Committee on November 12, 2003.

                                       35
<PAGE>

      D. No Limit on Other Compensation Arrangements. Nothing contained in the
Plan shall prevent the Company or any Affiliate from adopting or continuing in
effect other or additional compensation arrangements, and such arrangements may
be either generally applicable or applicable only in specific cases.

      E. No Right to Employment. The grant of an Award shall not be construed as
giving a Participant the right to be retained in the employ of the Company or
any Affiliate, nor will it affect in any way the right of the Company or an
Affiliate to terminate such employment at any time, with or without cause. In
addition, the Company or an Affiliate may at any time dismiss a Participant from
employment free from any liability or any claim under the Plan or any Award,
unless otherwise expressly provided in the Plan or in any Award Agreement.
Nothing in this Plan shall confer on any person any legal or equitable right
against the Company or any Affiliate, directly or indirectly, or give rise to
any cause of action at law or in equity against the Company or an Affiliate. The
Awards granted hereunder shall not form any part of the wages or salary of any
Eligible Person for purposes of severance pay or termination indemnities,
irrespective of the reason for termination of employment. Under no circumstances
shall any person ceasing to be an employee of the Company or any Affiliate be
entitled to any compensation for any loss of any right or benefit under the Plan
which such employee might otherwise have enjoyed but for termination of
employment, whether such compensation is claimed by way of damages for wrongful
or unfair dismissal, breach of contract or otherwise. By participating in the
Plan, each Participant shall be deemed to have accepted all the conditions of
the Plan and the terms and conditions of any rules and regulations adopted by
the Committee and shall be fully bound thereby.

      F. Governing Law. The validity, construction and effect of the Plan or any
Award, and any rules and regulations relating to the Plan or any Award, shall be
determined in accordance with the internal laws, and not the law of conflicts,
of the State of Delaware.

      G. Severability. If any provision of the Plan or any Award is or becomes
or is deemed to be invalid, illegal or unenforceable in any jurisdiction or
would disqualify the Plan or any Award under any law deemed applicable by the
Committee, such provision shall be construed or deemed amended to conform to
applicable laws, or if it cannot be so construed or deemed amended without, in
the determination of the Committee, materially altering the purpose or intent of
the Plan or the Award, such provision shall be stricken as to such jurisdiction
or Award, and the remainder of the Plan or any such Award shall remain in full
force and effect.

      H. No Trust or Fund Created. Neither the Plan nor any Award shall create
or be construed to create a trust or separate fund of any kind or a fiduciary
relationship between the Company or any Affiliate and a Participant or any other
Person. To the extent that any Person acquires a right to receive payments from
the Company or any Affiliate pursuant to an Award, such right shall be no
greater than the right of any unsecured general creditor of the Company or any
Affiliate.

      I. Other Benefits. No compensation or benefit awarded to or realized by
any Participant under the Plan shall be included for the purpose of computing
such Participant's compensation under any compensation-based retirement,
disability, or similar plan of the Company unless required by law or otherwise
provided by such other plan.

      J. No Fractional Shares. No fractional Shares shall be issued or delivered
pursuant to the Plan or any Award, and the Committee shall determine whether
cash shall be paid in lieu of any fractional Shares or whether such fractional
Shares or any rights thereto shall be canceled, terminated or otherwise
eliminated.

      K. Headings. Headings are given to the Sections and subsections of the
Plan solely as a convenience to facilitate reference. Such headings shall not be
deemed in any way material or relevant to the construction or interpretation of
the Plan or any provision thereof.

Section 10. Effective Date of the Plan.

      The Plan shall be effective on December 4, 2001 subject to approval by the
shareholders of the Company

                                       36
<PAGE>

on such date.

Section 11. Term of the Plan.

      No Award shall be granted under the Plan ten years after the effective
date or any earlier date of discontinuation or termination established pursuant
to Section 7A of the Plan. However, unless otherwise expressly provided in the
Plan or in an applicable Award Agreement, any Award theretofore granted may
extend beyond such date, and the authority of the Committee provided for
hereunder with respect to the Plan and any Awards, and the authority of the
Board to amend the Plan, shall extend beyond the termination of the Plan.

                                       37Exhibit 10.24

                                 AMENDMENT NO. 2
                             TO EMPLOYMENT AGREEMENT

            Enzon Pharmaceuticals, Inc., f/k/a Enzon, Inc. (the "Company") and
Arthur J. Higgins (the "Executive") agree to amend the Employment Agreement
between them dated as of May 9, 2001, and amended as of May 23, 2001 (the
"Agreement"), as follows:

1.    Section 9(d)(i) of the Agreement is hereby amended to read in its entirety
      as follows:

            "(i) "Board Change" which, for purposes of this Agreement, shall
            have occurred if, over any twenty-four month period, a majority of
            the seats (other than vacant seats) on the Company's Board were to
            be occupied by individuals who were neither (A) nominated by at
            least one-half (1/2) of the directors then in office (but excluding,
            for purposes of determining directors then in office, any director
            whose initial assumption of office occurs as a result of either an
            actual or threatened election contest, or other actual or threatened
            solicitation of proxies or consents by or on behalf of a Person (as
            defined herein) other than the Company or its board of directors);
            nor (B) appointed by directors so nominated, or"

2.    Section 9(d)(iii) of the Agreement is hereby amended to read in its
      entirety as follows:

            "(iii) a consolidation of the Company with another entity, or a
            merger of the Company with another entity in which neither the
            Company nor a corporation that, prior to the merger, was a
            subsidiary of the Company shall be the surviving entity; or"

3.    Section 10(g) of the Agreement is hereby amended as follows:

      (a)   Sections 10(g)(iv) and 10(g)(v) are hereby deleted.

      (b)   Section 10(g)(vi) is hereby renumbered as Section 10(g)(iv).

      (c)   The first sentence of the last paragraph of Section 10(g) is amended
            to read in its entirety as follows:

            "In the event the Executive becomes entitled to payments under this
            Section 10(g) and/or the accelerated vesting of options under
            Section 11 hereof, the Company shall cause its independent auditors
            promptly to review, at the Company's expense, the applicability of
            Section 4999 of the Internal Revenue Code (the "Code") to such
            payments and/or vesting."

4.    The Agreement is hereby amended by adding a new Section 11 thereto, which
      shall read as follows:

            11.   Effect of Change of Control. In the event of a Change of
                  Control, in addition to any other consequences provided for in
                  this Agreement,

                  (a)   all shares of restricted stock and restricted stock
                        units awarded to Executive shall fully vest immediately
                        prior to the Change of Control; and

                  (b)   all options to acquire shares of the Company held by the
                        Executive shall become

                                       38
<PAGE>

                        fully vested immediately prior to the effective date of
                        the Change of Control. Executive shall have a reasonable
                        opportunity to exercise all or any portion of such
                        options prior to the effective date of the Change of
                        Control, and any options not exercised prior to the
                        effective date of the Change of Control shall terminate
                        as of the effective date of the Change of Control and
                        will be of no further force or effect. To the extent
                        that this Section 11 is inconsistent with the provisions
                        of the relevant plan and granting instruments under
                        which such options were issued, the Company and
                        Executive agree that such inconsistent provisions are
                        hereby superceded and the provisions of this Section 11
                        shall govern.

5.    The Agreement is hereby further amended by renumbering original Section 11
      as Section 12. All references in the Agreement originally to Section 11
      shall be changed to be references to Section 12.

6.    Except as amended hereby, the Agreement shall remain in full force and
      effect. This Amendment may be executed in counterparts and each of such
      counterparts shall for all purposes be deemed to be an original, and such
      counterparts shall together constitute one and the same instrument. The
      parties hereto have executed this Amendment as of December 3, 2003.

                         ENZON PHARMACEUTICALS, INC.

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

                         By:    /s/ Arthur J. Higgins
                            ---------------------------------------------------

                                       39

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