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                                                                 EXHIBIT  10.91

                              SEPARATION AGREEMENT
                               (SAMUEL D. WAKSAL)

                  SEPARATION AGREEMENT, dated as of May 22, 2002 ("Agreement"),
between IMCLONE SYSTEMS INCORPORATED, a Delaware corporation (the "Company"),
and SAMUEL D. WAKSAL (the "Executive"). Capitalized terms used herein but not
defined herein shall have the meanings given to them in the Employment
Agreement, dated as of September 19, 2001 (the "Employment Agreement"), between
the Company and the Executive.

SECTION 1. RESIGNATION. In consideration of the Company's agreements hereunder,
the Executive hereby resigns from all directorships, offices and positions with
the Company and its subsidiaries, affiliates and employee benefit plans and
trusts, effective May 22, 2002 (the "Date of Termination"). The Executive and
the Company hereby agree that the Employment Period shall be terminated as of
the Date of Termination.

SECTION 2. SEPARATION COMPENSATION. Within five (5) days following the Date of
Termination, the Company shall pay to Executive $7,000,000 (seven million
dollars).

SECTION 3. OTHER BENEFITS.

                (a) The Company shall maintain in full force and effect, for the
        continued benefit of Executive, his spouse and his dependents for a
        period of three (3) years following the Date of Termination the medical,
        hospitalization, dental, and life insurance programs in which Executive,
        his spouse and his dependents were participating immediately prior to
        the Date of Termination at the level in effect and upon substantially
        the same terms and conditions (including without limitation
        contributions required by Executive for such benefits) as existed
        immediately prior to the Date of Termination; provided, that, if
        Executive, his spouse or his dependents cannot continue to participate
        in the Company programs providing such benefits, the Company shall
        arrange to provide Executive, his spouse and his dependents with the
        economic equivalent of such benefits which they otherwise would have
        been entitled to receive under such plans and programs ("Continued
        Benefits"), provided, that, such Continued Benefits shall terminate on
        the date or dates Executive receives equivalent coverage and benefits,
        without waiting period or pre-existing condition limitations, under the
        plans and programs of a subsequent employer (such coverage and benefits
        to be determined on a coverage-by-coverage or benefit-by-benefit,
        basis).

                (b) Subject to the Executive's insurability, the Company shall
        purchase for the benefit of Executive or his designated beneficiaries a
        term life insurance policy with a death benefit of $5,000,000 to be
        maintained for 6 years following the Date of Termination.

                (c) The Company shall reimburse Executive in the manner provided
        in Section 5 of the Employment Agreement for reasonable expenses
        incurred, but not paid prior to the Date of Termination.
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                (d) The Executive shall be entitled to any other rights,
        compensation and/or benefits as may be due to the Executive as of the
        Date of Termination in accordance with the terms and provisions of any
        agreements (other than the Employment Agreement), plans or programs of
        the Company.

                (e) With respect to equity awards granted or made on or after
        September 19, 2001, notwithstanding the terms or conditions of any stock
        option, stock appreciation right, restricted stock or similar agreements
        between the Company and Executive to the contrary, and for purposes
        thereof, such agreements shall be deemed to be amended in accordance
        with this Section 3(e) if need be as of the Date of Termination and
        neither the Company, the Board nor the Committee shall take or assert
        any position contrary to the foregoing, such that Executive shall vest,
        as of the Date of Termination, in all rights under such agreements
        (e.g., stock options that would otherwise vest after the Date of
        Termination) and in the case of stock options, stock appreciation rights
        or similar awards, thereafter shall be permitted to exercise any and all
        such rights until the end of the term of such awards (regardless of any
        termination of employment restrictions therein contained) and restricted
        stock held by Executive shall become immediately vested as of the Date
        of Termination.

                (f) The Executive shall have the right to receive in connection
        with this Agreement any payments to which the Executive would have been
        entitled pursuant to Section 8(e) of the Employment Agreement.

                (g) The Company shall pay fees of the Executive's crisis
        management consultant incurred during the six months following the Date
        of Termination; provided that such fees do not exceed $25,000 per month.

                (h) The Company shall pay to the applicable advisors of the
        Executive, the Executive's legal fees incurred in connection with the
        negotiation of this Agreement up to a maximum of $35,000.

SECTION 4. RESTRICTIVE COVENANTS.

                (a) CONFIDENTIALITY. The Executive shall not, without the prior
        written consent of the Company or as may otherwise be required by
        applicable law or legal process, or as is necessary in connection with
        any adversarial proceeding against the Company (in which cases Executive
        shall use his reasonable best efforts in cooperating with the Company in
        obtaining a protective order against disclosure by a court of competent
        jurisdiction) at any time use, divulge or convey any trade secrets or
        confidential information, knowledge or data relating to the Company or
        its affiliates and their respective businesses and investments
        (including information, knowledge or data of third parties as to which
        the Company or an affiliate is under an obligation of confidentiality),
        which is not generally available public knowledge (other than
        information that became public knowledge as a result of acts by
        Executive in violation of this Agreement).

                (b) NON-SOLICITATION. The Executive hereby agrees, in
        consideration of the payments to him hereunder, that from the Date of
        Termination through the first
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        anniversary of the Date of Termination, Executive shall not directly or
        indirectly induce any employee of the Company to terminate such
        employment or to become employed by any other biopharmaceutical company.

                (c) NON-COMPETITION. The Executive hereby agrees, in
        consideration of the payments to him hereunder, that from the Date of
        Termination through the first anniversary of the Date of Termination, he
        shall not be employed by or perform activities on behalf of, or have an
        ownership interest in, any person, firm, corporation or other entity, or
        in connection with any business enterprise, that is directly or
        indirectly engaged in any of the biopharmaceutical businesses in which
        the Company and its subsidiaries have significant involvement (other
        than by means of Executive's direct or beneficial ownership of up to one
        percent (1%) of any entity whether or not such entity is in the same or
        competing business); provided that nothing in this Section 4(c) shall
        restrict the Executive's current relationships with Scientia Health
        Group Inc., Antigenics, Cibus Genetics LLC, Berleley Heart Lab,
        Microbes, Prototek II, Inc., Tribeca Pharmaceutical Corporation and
        Valigen, N.V.

                (d) BLUE PENCIL. The parties hereby acknowledge that the
        restrictions in this Section 4 have been specifically negotiated and
        agreed to by the parties hereto and are limited only to those
        restrictions necessary to protect the Company and its subsidiaries from
        the misuse of confidential information and unfair competition. The
        parties hereby agree that if the scope or enforceability of any
        provision, paragraph or subparagraph of this Section 4 is in any way
        disputed at any time, and should a court find that such restrictions are
        overly broad, the court may modify and enforce the covenant to the
        extent that it believes it to be reasonable under the circumstances.
        Each provision, paragraph and subparagraph of this Section 4 is
        separable from every other provision, paragraph, and subparagraph and
        constitutes a separate and distinct covenant. Executive acknowledges
        that the Company's business is not limited by geographical scope, is
        operating throughout the world and that the effect of Section 4(c) may
        be to prevent him from working in a competitive business after his
        termination of employment hereunder.

SECTION 5. SPECIFIC PERFORMANCE. The Executive acknowledges and agrees that the
Company's remedies at law for a breach or threatened breach of any of the
provisions of Section 4 would be inadequate and the Company would suffer
irreparable damages as a result of such breach or threatened breach. In
recognition of this fact, the Executive agrees that, in the event of such a
breach or threatened breach, in addition to any remedies at law, the Company,
without posting any bond, shall, notwithstanding Section 17 of this Agreement,
be entitled to bring an action in any court of competent jurisdiction for the
purpose of obtaining equitable relief in the form of specific performance,
temporary restraining order, temporary or permanent injunction or any other
equitable remedy which may then be available.

SECTION 6. COOPERATION. The Executive shall provide reasonable cooperation in
connection with any action, investigation or proceeding which relates to the
Company or any of its affiliates, including without limitation in connection
with any litigation and disputes arising out of actions or inactions of the
Company or any affiliate of which the Executive has knowledge or information;
provided that such cooperation does not unreasonably interfere with the
Executive's other pursuits or undertakings. The Executive further agrees to
cooperate with the Company in supplying data, information, and expertise within
the Executive's special knowledge or competence and otherwise assist the Company
in the protection of the interests of the Company
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and its affiliates; provided that such cooperation does not unreasonably
interfere with the Executive's other pursuits or undertakings. The Company shall
reimburse the Executive for reasonable out-of-pocket expenses incurred by the
Executive in connection with such cooperation following its receipt of the
Executive's appropriately itemized request.

SECTION 7. INDEMNITY. The existing rights of the Executive and obligations of
the Company with regard to indemnification of the Executive that are not
dependent upon Executive's continued employment or holding an office or
directorship with the Company or an affiliate, and the indemnification rights
under the Company's current certificate of incorporation and by-laws, shall
continue.

SECTION 8. NON-DISPARAGEMENT. The Company and its affiliates shall refrain from
making any statements or comments of a defamatory or disparaging nature to any
third party regarding the Executive, and the Executive shall refrain from making
any statements or comments of a defamatory or disparaging nature to any third
party regarding the Company, any of its affiliates, or any of their directors,
officers, personnel, policies or product; provided, however, that it shall not
be a violation of this Section 8 for either party to make truthful statements
when required to do so by a court of law, by any governmental agency having
supervisory authority over the party, or by any administrative or legislative
body with apparent jurisdiction to order the party to divulge, disclose or make
accessible such information or as may otherwise be required to defend any
allegations or statements made by the other party.

SECTION 9. SEVERABILITY. In the event that any one or more of the provisions of
this Agreement shall be or become invalid, illegal or unenforceable in any
respect, the validity, legality and enforceability of the remaining provisions
of this Agreement shall not be affected thereby.

SECTION 10. ASSIGNMENT. This Agreement, and all of Executive's rights and duties
hereunder, shall not be assignable or delegable by Executive. Any purported
assignment or delegation by Executive in violation of the foregoing shall be
null and void ab initio and of no force and effect. This Agreement may be
assigned by the Company to a person or entity which is a successor in interest
to substantially all of the business operations of the Company. Upon such
assignment, the rights and obligations of the Company hereunder shall become the
rights and obligations of such successor person or entity.

SECTION 11. NO MITIGATION. Executive shall not be required to mitigate the
amount of any payment provided for pursuant to this Agreement by seeking other
employment, and, except as may be required pursuant to Section 3(a) of this
Agreement, the Executive shall not be required to pay the Company any amounts
the Executive may receive from such alternative employment. Additionally,
amounts owed to the Executive under this Agreement shall not be offset by any
claims the Company may have against the Executive.

SECTION 12. SUCCESSORS; BINDING AGREEMENT. This Agreement shall inure to the
benefit of and be binding upon personal or legal representatives, executors,
administrators, successors, heirs, distributees, devisees and legatees.

SECTION 13. NOTICE. For purposes of this Agreement, notices and all other
communications provided for in this Agreement shall be in writing and shall be
deemed to have been duly given when delivered by hand or overnight courier or
three days after it has been mailed by United States registered mail, return
receipt requested, postage prepaid, addressed to the respective
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addresses set forth below in this Agreement, or to such other address as either
party may have furnished to the other in writing in accordance herewith, except
that notice of change of address shall be effective only upon receipt.

                  Notice to the Company shall be addressed to:

                           ImClone Systems Incorporated
                           180 Varick Street
                           New York, New York 10014
                           Attn:  Chief Financial Officer


                  Notice to the Executive shall be addressed to:

                           Dr. Samuel D. Waksal
                           150 Thompson Street, Apt. 5C
                           New York, NY 10012


SECTION 14. WITHHOLDING TAXES. The Company may withhold from any amounts payable
under this Agreement such Federal, state and local taxes as may be required to
be withheld pursuant to any applicable law or regulation.

SECTION 15. ENTIRE AGREEMENT/AMENDMENTS. This Agreement contains the entire
understanding of the parties with respect to the subject matter hereof and
supersedes the Employment Agreement, which shall terminate as of the date
hereof. For the avoidance of doubt, the Discovery and Non-Disclosure Agreement,
dated as of July 15, 1986, between the Company and the Executive shall survive.
This Agreement may not be amended except by written instrument signed by the
parties hereto.

SECTION 16. NO WAIVER. The failure of a party to insist upon strict adherence to
any term of this Agreement on any occasion shall not be considered a waiver of
such party's rights or deprive such party of the right thereafter to insist upon
strict adherence to that term or any other term of this Agreement.

SECTION 17. ARBITRATION. Except as set forth in Section 5 of this Agreement, any
dispute, controversy or claim arising out of or relating to this Agreement shall
be settled exclusively by binding arbitration for resolution in New York, New
York in accordance with the rules and procedures of the Employment Dispute
Resolution Rules of the American Arbitration Association. The decision of the
arbitrator shall be final and binding on both parties, and any court of
competent jurisdiction may enter judgment upon the award. The Company shall pay
all expenses relating to such arbitration, including but not limited to, the
Executive's legal fees and expenses, regardless of outcome, unless the
arbitrator determines that the Executive has acted in bad faith.

SECTION 18. GOVERNING LAW; VENUE. This Agreement shall be governed by and
construed in accordance with the laws of the State of New York, without regard
to conflicts of laws principles thereof. Except as provided in Section 17 of
this Agreement, the Executive irrevocably submits to the non-exclusive
jurisdiction of the courts of the State of New York and the courts of the United
States located in the State of New York for the purpose of any action or
proceeding
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arising out of or relating to this Agreement, and acknowledges that the
designated fora have a reasonable relation to this Agreement and the parties'
relationship to one another.

SECTION 19. COUNTERPARTS. This Agreement may be signed in counterparts, each of
which shall be an original, with the same effect as if the signatures thereto
and hereto were upon the same instrument.

                   IN WITNESS WHEREOF, the parties hereto have executed this
Agreement as of the day and year first written above.

                                                 IMCLONE SYSTEMS INCORPORATED


                                                 /S/ Daniel S. Lynch
                                                 ------------------------------
                                                 BY:  DANIEL S. LYNCH
                                                 TITLE: CFO


                                                 /S/ Samuel D. Waksal, Ph.D.
                                                 ------------------------------
                                                 SAMUEL D. WAKSAL, PH.D.