Exhibit 23.1


               CONSENT OF ERNST & YOUNG LLP, INDEPENDENT AUDITORS



                We consent to the incorporation by reference in the Registration
Statements (Form S-8 Nos. 333-11759, 333-32785, 333-58999, 333-86383, 333-44784,
333-72636, 333-72644, and 333-73430) pertaining to the 1993 Amended Incentive
Stock Plan, the 1996 Employee Stock Purchase Plan, the 1996 Director Option
Plan, the 2001 Incentive Stock Plan, and The Althexis Company, Inc. 1999 Stock
Option Plan and (Form S-3 Nos. 333-73890 and 333-55318) and related
Prospectuses, of our report dated February 3, 2003, except for Note 1 and the
last paragraph of Note 10, as to which the date is March 20, 2003, with respect
to the consolidated financial statements of Essential Therapeutics, Inc.
(formerly Microcide Pharmaceuticals, Inc.) included in the Annual Report (Form
10-K) for the year ended December 31, 2002.


/s/ ERNST & YOUNG LLP

Boston, Massachusetts
March 27, 2003