EXHIBIT 32.1

                           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 Quarterly Report of ImClone Systems Incorporated
(the "Company") on Form 10-Q for the period ended June 30, 2003 as filed with
the Securities and Exchange Commission on the date hereof (the "Report"), I,
Daniel S. Lynch, Senior Vice President and Chief Administrative Officer, 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
                                          --------------------------------------
                                                     Daniel S. Lynch
                                              Acting Chief Executive Officer

August 13, 2003