EXHIBIT 99.12

                            CERTIFICATION PURSUANT TO
                             18 U.S.C. SECTION 1350,
                             AS ADOPTED PURSUANT TO
                  SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

In connection with this Amendment No. 1 to the Quarterly Report of ImClone
Systems Incorporated (the "Company") on Form 10-Q for the period ended September
30, 2002 as filed with the Securities and Exchange Commission on the date hereof
(the "Report"), I, Michael J. Howerton, Vice President, Finance and Business
Development, Secretary and Acting Chief Financial Officer of the Company,
certify, pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906
of the Sarbanes-Oxley Act of 2002, that:

    (1) The Report fully complies with the requirements of Section 13(a) or
        15(d) of the Securities Exchange Act of 1934; and

    (2) The information contained in the Report fairly presents, in all material
        respects, the financial condition and results of operations of the
        Company.

/S/ MICHAEL J. HOWERTON
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Michael J. Howerton
Acting Chief Financial Officer
June 23, 2003