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                                                                   EXHIBIT 99.4

                          IMCLONE SYSTEMS INCORPORATED
                1998 EMPLOYEE STOCK PURCHASE PLAN, AS AMENDED(1)

         The following constitutes the provisions of the 1998 Employee Stock
Purchase Plan of ImClone Systems Incorporated.

1.       PURPOSE.

         The purpose of the Plan is to provide employees of the Company and its
         Affiliates with an opportunity to purchase Common Stock of the Company.
         It is the intention of the Company that the Options granted under the
         Plan be considered options issued under an "Employee Stock Purchase
         Plan" as that term is defined under Section 423(b) of the Code. The
         provisions of the Plan shall, accordingly, be construed so as to extend
         and limit participation in a manner consistent with the requirements of
         that section of the Code.

2.       DEFINITIONS.

(a)      "AFFILIATE" as used in the Plan means any parent corporation or
         subsidiary corporation of the Company, as those terms are defined in
         Sections 424(e) and (f), respectively, of the Code.

(b)      "BOARD" shall mean the Board of Directors of the Company, or a
         committee of the Board of Directors named by the Board to administer
         the Plan.

(c)      "CODE" shall mean the Internal Revenue Code of 1986, as amended.

(d)      "COMMON STOCK" shall mean the Common Stock, $0.001 par value, of the
         Company.

(e)      "COMPANY" shall mean ImClone Systems Incorporated, a Delaware
         corporation.

(f)      "COMPENSATION" shall mean all compensation that is taxable income for
         federal income tax purposes, including, payments for overtime, shift
         premium, incentive compensation, incentive payments, bonuses,
         commissions and other compensation.

(g)      "CONTINUOUS STATUS AS AN EMPLOYEE" shall mean the absence of any
         interruption or termination of service as an employee of the Company or
         any Affiliate. Continuous Status as an Employee shall not be considered
         interrupted in the case of a leave of absence agreed to in writing by
         the Company or any Affiliate, provided that such leave is for a period
         of not more than 90 days or reemployment upon the expiration of such
         leave is guaranteed by contract or statute.

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(1) This Plan was amended by the Board on March 29, 1999.
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(h)      "CONTRIBUTIONS" shall mean all amounts credited to the account of a
         participant pursuant to the Plan.

(i)      "EXERCISE DATE" shall mean the last day of each Offering Period of the
         Plan.

(j)      "OFFERING DATE" shall mean the first business day of an Offering Period
         under the Plan.

(k)      "OFFERING PERIOD" shall mean any of the three month periods commencing
         on each of July 1, October 1, January 1 and April 1 of each year (or
         such other periods as may be determined by the Board which shall comply
         with Section 423(b)(7) of the Code); provided that the initial offering
         period shall commence at a time to be determined by the Board.

(l)      "OPTION" shall mean an option granted under Section 6 of this Plan.

(m)      "PLAN" shall mean this ImClone Systems Incorporated 1998 Employee Stock
         Purchase Plan.

3.       ELIGIBILITY.

(a)      Options may be granted only to employees of the Company or any
         Affiliate. An employee of the Company or any Affiliate shall be
         eligible to participate in the Plan upon commencement of employment
         with the Company; provided, that no employee of the Company or any
         Affiliate shall be eligible to be granted an Option under the Plan,
         unless, on the Offering Date of such Offering Period, such employee's
         customary employment with the Company or such Affiliate is at least
         twenty (20) hours per week and at least five (5) months per calendar
         year.

(b)      No employee shall be eligible for the grant of an Option under the Plan
         if, immediately after any such grant, such employee owns stock
         possessing five percent (5%) or more of the total combined voting power
         or value of all classes of stock of the Company or of any Affiliate.
         For purposes of this subparagraph 3(b), the rules of Section 424(d) of
         the Code shall apply in determining the stock ownership of any
         employee, and stock which such employee may purchase under all
         outstanding rights and options shall be treated as stock owned by such
         employee.

(c)      An eligible employee may be granted an Option under the Plan only if
         such Option, together with any other options granted under "employee
         stock purchase plans" of the Company and any Affiliates, as specified
         by Section 423(b)(8) of the Code, do not permit such employee's rights
         to purchase stock of the Company or any Affiliate to accrue at a rate
         which exceeds twenty-five thousand dollars ($25,000) of fair market
         value of such stock (determined at the time such Options are granted)
         for each calendar year in which such Options are outstanding at any
         time. Any Option granted under the Plan shall be deemed to be modified
         to the extent necessary to satisfy this paragraph 3(c).

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(d)      Officers of the Company shall be eligible to participate in the Plan;
         provided, however, that the Board may provide in an Offering Period
         that certain employees who are highly compensated employees within the
         meaning of Section 423(b)(4)(D) of the Code shall not be eligible to
         participate.

4.       OFFERING PERIODS.

         The Plan shall be implemented by a series of Offering Periods, with a
         new Offering Period commencing on July 1, October 1, January l and
         April 1 of each year (or such other periods as may be determined by the
         Board which shall comply with Section 423(b)(7) of the Code); provided
         that the initial Offering Period shall commence at a time to be
         determined by the Board. The Plan shall continue until terminated in
         accordance with paragraph 17 or paragraph 21 hereof. In addition,
         employees shall not be entitled to enroll in the Plan or exercise any
         Options granted under the Plan during any period in which the Company
         has restricted the purchase or sale of its securities by its employees.

5.       PARTICIPATION; CONTRIBUTIONS.

(a)      An eligible employee may become a participant in the Plan by completing
         an enrollment form ("Enrollment Form") provided by the Company and
         filing it with the Company prior to the applicable Offering Date,
         unless a later time for filing the Enrollment Form is set by the Board
         for all eligible employees with respect to a given Offering Period. The
         Enrollment Form shall set forth the percentage of the participant's
         Compensation (which shall be a whole percentage not less than 1% and
         not more than 15%) to be paid as Contributions pursuant to the Plan.

(b)       Payroll deductions shall commence on the first payroll following the
          Offering Date and shall end on the last payroll paid on or prior to
          the Exercise Date of the Offering Period to which the Enrollment Form
          is applicable, unless sooner terminated by the participant as provided
          in paragraph 8. All payroll deductions made by a participant shall be
          credited to such participant in an account under the Plan. A
          participant may not make payments into such account.

(c)      A participant may discontinue his or her participation in the Plan as
         provided in paragraph 8.

(d)      Notwithstanding the foregoing, to the extent necessary to comply with
         Section 423(b)(8) of the Code and paragraph 3(c) herein, a
         participant's payroll deductions may be decreased to 0% at such time
         during any Offering Period which is scheduled to end during the current
         calendar year that the aggregate of all payroll deductions accumulated
         with respect to such Offering Period and any other Offering Period
         ending within the same calendar year equals $21,250. Payroll deductions
         shall recommence at the rate provided in such participant's Enrollment
         Form at the beginning of the first Offering



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         Period which is scheduled to end in the following calendar year, unless
         terminated by the participant as provided in paragraph 8.

6.       GRANT OF OPTION.

(a)      On the Offering Date of each Offering Period, each eligible employee
         participating in such Offering Period shall be granted an Option to
         purchase on the Exercise Date of such Offering Period a number of
         shares of Common Stock determined by dividing such employee's
         Contributions accumulated prior to such Exercise Date and retained in
         the participant's account as of the Exercise Date by 85% of the fair
         market value of a share of the Common Stock on the Exercise Date;
         provided however, that such purchase shall be subject to the
         limitations set forth in Sections 3(b), 3 (c), 3(d) and 10 hereof. The
         fair market value of a share of the Common Stock shall be determined as
         provided in Section 6(b) below.

(b)      The fair market value of the Common Stock on a given date shall be
         determined by the Board in its discretion; provided that (i) if the
         Common Stock is listed on a stock exchange, the fair market value per
         share shall be the closing price on such exchange on such date as
         reported in the Wall Street Journal (or, (A) if not so reported, as
         otherwise reported by the exchange, and (B) if not reported on such
         date, then on the last prior date on which a sale of the Common Stock
         was reported); or (ii) if not listed on an exchange but traded on the
         National Association of Securities Dealers Automated Quotation
         ("Nasdaq") National Market, the fair market value per share shall be
         the last reported sale price on such date as reported in the Wall
         Street Journal (or (A) if not so reported, as otherwise reported by the
         Nasdaq National Market and (B) if not reported on such date, then on
         the last prior date on which a sale of the Common Stock was reported)
         or (iii) if traded on Nasdaq SmallCap and not the National Market the
         fair market value per share shall be the mean of the closing bid and
         asked price per share of the Common Stock on such date, as reported in
         the Wall Street Journal (or, (A) if not so reported, as otherwise
         reported by Nasdaq, and (B) if not so reported on such date, then on
         the last prior date on which a sale of the Common Stock was reported);
         or (iv) if the Common Stock is otherwise publicly traded, but not
         listed on a stock exchange or traded on Nasdaq, the fair market value
         per share shall be determined in good faith by the Board in its
         discretion.

7.       EXERCISE OF OPTION.

(a)      Unless a participant withdraws from the Plan as provided in paragraph
         8, such participant's Option for the purchase of shares of Common Stock
         will be exercised automatically on the Exercise Date of the Offering
         Period and the maximum number of full shares of Common Stock subject to
         the Option will be purchased for such participant at the applicable
         purchase price with the accumulated Contributions in such participant's
         account. If a fractional number of shares of Common Stock results, then
         such number shall be rounded down to the next whole number and the
         excess Contributions shall be carried forward to the next Exercise
         Date, unless such participant withdraws the Contributions pursuant to
         paragraph 8(a) or is no longer eligible to participate in the Plan, in
         which case such amount shall be distributed to the participant without
         interest. The

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         shares purchased upon exercise of an Option hereunder shall be deemed
         to be transferred to the participant on the Exercise Date. During a
         participant's lifetime, a participant's Option to purchase shares
         hereunder is exercisable only by such participant.

(b)      Shares shall not be issued with respect to an Option unless the
         exercise of such Option and the issuance and delivery of such shares of
         Common Stock pursuant thereto shall comply with all applicable
         provisions of law, domestic or foreign, including, without limitation,
         the Securities Act of 1933, as amended, the Securities Exchange Act of
         1934, as amended, the rules and regulations promulgated thereunder, and
         the requirements of any stock exchange upon which the shares of Common
         Stock may then be listed, and shall be further subject to the approval
         of counsel for the Company with respect to such compliance. As a
         condition to the exercise of an Option, the Company may require the
         person exercising such Option to represent and warrant at the time of
         any such exercise that the shares of Common Stock are being purchased
         only for investment and without any present intention to sell or
         distribute such shares of Common Stock if, in the opinion of counsel
         for the Company, such a representation is required by any of the
         aforementioned applicable provisions of law.

8.       WITHDRAWAL; TERMINATION OF EMPLOYMENT.

(a)      A participant may withdraw all but not less than all the Contributions
         credited to his or her account under the Plan at any time prior to the
         Exercise Date of the Offering Period by written notice to the Company.
         All of the participant's Contributions credited to such participant's
         account will be paid to such participant promptly after receipt of such
         participant's notice of withdrawal and such participant's Option for
         the current Offering Period will be automatically terminated, and no
         further Contributions for the purchase of shares of Common Stock will
         be made during the Offering Period.

(b)      Upon termination of the participant's Continuous Status as an Employee,
         prior to the Exercise Date of the Offering Period for any reason,
         including retirement or death, the Contributions credited to such
         participant's account will be returned to such participant or, in the
         case of his or her death, to the person or persons entitled thereto
         under paragraph 12, and his or her Option will be automatically
         terminated.

(c)      In the event an employee fails to remain in Continuous Status as an
         Employee of the Company for at least 20 hours per week during the
         Offering Period in which the employee is a participant, such
         participant will be deemed to have elected to withdraw from the Plan
         and the Contributions credited to such participant's account will be
         returned to such participant and the Option terminated.

(d)      A participant's withdrawal from an Offering Period will not have any
         effect upon his or her eligibility to participate in a succeeding
         Offering Period or in any similar plan which may hereafter be adopted
         by the Company.

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9.       INTEREST.

         No interest shall accrue on the Contributions of a participant in the
         Plan.

10.      STOCK.

         The maximum number of shares of Common Stock which shall be made
         available for sale under the Plan shall be 500,000 shares subject to
         adjustment upon changes in capitalization of the Company as provided in
         paragraph 16. Shares sold under the Plan may be newly issued shares or
         shares reacquired in private transactions or open market purchases, but
         all shares sold under the Plan regardless of source shall be counted
         against the 500,000 share limitation. If the total number of shares of
         Common Stock which would otherwise be subject to Options granted
         pursuant to Section 6(a) hereof on the Offering Date of an Offering
         Period exceeds the number of shares of Common Stock then available
         under the Plan (after deduction of all shares of Common Stock for which
         Options have been exercised or are then outstanding), the Company shall
         make a pro rata allocation of the shares of Common Stock remaining
         available for Option grant in as uniform a manner as shall be
         reasonably practicable and as it shall determine to be equitable. Any
         amounts remaining in an employee's account not applied to the purchase
         of Common Stock pursuant to this Section 10 shall be refunded on or
         promptly after the Exercise Date. In such event, the Company shall give
         written notice of such reduction of the number of shares of Common
         Stock subject to the Option to each employee affected thereby and shall
         similarly reduce the rate of Contributions, if necessary.

11.      ADMINISTRATION.

         The Board shall supervise and administer the Plan and shall have full
         power to adopt, amend and rescind any rules deemed desirable and
         appropriate for the administration of the Plan and not inconsistent
         with the Plan, to construe and interpret the Plan, and to make all
         other determinations necessary or advisable for the administration of
         the Plan.

12.      DESIGNATION OF BENEFICIARY.

(a)      A participant may file a written designation of a beneficiary who is to
         receive any shares of Common Stock and cash, if any, from the
         participant's account under the Plan in the event of such participant's
         death subsequent to the end of the Offering Period but prior to
         delivery of such participant's shares of Common Stock and cash. In
         addition, a participant may file a written designation of a beneficiary
         who is to receive any cash from the participant's account under the
         Plan in the event of such participant's death prior to the Exercise
         Date of the Offering Period. If a participant is married and the
         designated beneficiary is not the spouse, spousal consent shall be
         required for such designation to be effective.

(b)      Such designation of beneficiary may be changed by the participant (and
         his or her spouse, if any) at any time by written notice. In the event
         of the death of a participant and in the

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         absence of a beneficiary validly designated under the Plan who is
         living at the time of such participant's death, the Company shall
         deliver such shares of Common Stock and/or cash to the executor or
         administrator of the estate of the participant, or if no such executor
         or administrator has been appointed (to the knowledge of the Company),
         the Company, in its discretion, may deliver such shares and/or cash to
         the spouse or to any one or more dependents or relatives of the
         participant, or if no spouse, dependent or relative is known to the
         Company, then to such other person as the Company may designate.

13.      TRANSFERABILITY.

         Neither Contributions credited to a participant's account nor any
         rights with regard to the exercise of an Option or to receive shares
         under the Plan may be assigned, transferred, pledged or otherwise
         disposed of in any way other than by will, the laws of descent and
         distribution or as provided in paragraph 12 hereof by the participant.
         Any such attempt at assignment, transfer, pledge or other disposition
         shall be without effect, except that the Company may treat such act as
         an election to withdraw Contributions in accordance with paragraph 8.

14.      USE OF FUNDS.

         All Contributions received or held by the Company under the Plan may be
         used by the Company for any corporate purpose, and the Company shall
         not be obligated to segregate such Contributions.

15.      REPORTS.

         Individual accounts will be maintained for each participant in the
         Plan. Statements of account will be given to participants, the per
         share purchase price, the number of shares purchased and the remaining
         cash balance, if any.

16.      ADJUSTMENTS UPON CHANGES IN STOCK.

         If any change is made in the shares of Common Stock subject to the Plan
         or subject to any Option granted under the Plan (through merger,
         consolidation, reorganization, distribution of substantially all of the
         assets of the Company, spin-off of a subsidiary's voting securities to
         the Company's shareholders, recapitalization, stock dividend, split-up,
         combination of shares, exchange of shares, issuance of rights to
         subscribe, or change in capital structure), appropriate adjustments
         shall be made by the Board as to the maximum number of shares subject
         to the Plan and the number of shares and price per share subject to
         outstanding Options as shall be equitable to prevent dilution or
         enlargement of Option rights. Any determination made by the Board
         hereunder shall be final, binding and conclusive upon each participant.

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7.      AMENDMENT OR TERMINATION.

         The Board may at any time terminate or amend the Plan. Except as
         provided in paragraph 16, no such termination may affect Options
         previously granted, nor may an amendment make any change in any Option
         therefore granted which adversely affects the rights of any
         participant. In addition, to the extent necessary to comply with
         Section 423 of the Code (or any successor rule or provision or any
         applicable law or regulation), the Company shall obtain stockholder
         approval in such a manner and to such a degree as so required.

18.      NOTICES.

         All notices or other communications by a participant to the Company
         under or in connection with the Plan shall be deemed to have been duly
         given when received in the form specified by the Company at the
         location, or by the person, designated by the Company for the receipt
         thereof.

19.      RIGHT TO TERMINATE EMPLOYMENT.

         Nothing in the Plan or in any agreement entered into pursuant to the
         Plan shall confer upon any participant the right to continue in the
         employment of the Company or any Affiliate, or affect any right which
         the Company or any Affiliate may have to terminate the employment of
         such participant.

20.      RIGHTS AS A STOCKHOLDER.

         Neither the granting of an Option nor a deduction from payroll shall
         constitute a participant the owner of shares covered by an Option. No
         participant shall have any right as a stockholder unless and until an
         Option has been exercised, and the shares of Common Stock underlying
         the Option have been registered in the Company's share register.

21.      TERM OF PLAN.

         The Plan shall become effective upon its adoption by each of the Board
         and the stockholders and shall continue in effect for a term of ten
         (10) years unless sooner terminated earlier under paragraph 17.

22.      APPLICABLE LAW.

         This Plan shall be governed in accordance with the laws of Delaware.

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