X0202 4/A 2006-05-02 2006-05-05 1 0000765258 IMCLONE SYSTEMS INC IMCL 0001132625 VIKING GLOBAL PERFORMANCE LLC 55 RAILROAD AVENUE GREENWICH CT 06830 0 0 0 1 See Explanation of Responses The Form 4 initially filed on May 5, 2006, and thereafter amended on May 8, 2006 is hereby further amended to reflect that none of Viking Global Performance LLC, O. Andreas Halvorsen or David C. Ott has or had a pecuniary interest with respect to the options of ImClone Systems Incorporated ("Company") reported to be beneficially owned by Dr. Alexander J. Denner ("Dr. Denner"), a Director to the Company. Dr. Denner ceased to be employed by Viking Global Investors LP as of May 16, 2006 and no longer serves as a portfolio manager for Viking Global Performance LLC which acts as (i) the general partner of Viking Global Equities LP, a Delaware limited partnership, and (ii) investment manager to VGE III Portfolio Ltd., a Cayman Islands company. /s/ O. Andreas Halvorsen 2003-05-16