EXHIBIT 99.1

                            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 March 31,
2002 as filed with the Securities and Exchange Commission on the date hereof
(the "Report"), I, Daniel S. Lynch, Senior Vice President, Chief Administrative
Officer and Acting Chief Executive 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/ DANIEL S. LYNCH
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Daniel S. Lynch
Acting Chief Executive Officer
June 23, 2003