Alexion Pharmaceuticals (ALXN) 10-Q/A 2004 Q0 Quarterly report (amended)

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 the Amendment No. 1 to the quarterly report on Form 10-Q of Alexion Pharmaceuticals, Inc. (the “Company”) for the period ended January 31, 2004 as filed with the Securities and Exchange Commission on the date hereof (the “Report”), the undersigned, Leonard Bell M.D., Chief Executive Officer of the Company, hereby certifies, pursuant to 18 U.S.C. Section 1350, 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.

Dated: March 30, 2004	/s/ Leonard Bell, M.D.
	Leonard Bell, M.D.
	Chief Executive Officer

A signed original of this written statement required by Section 906 has been provided to the Company and will be retained by the Company and furnished to the Securities and Exchange Commission or its staff upon request.