Exhibit 10.1

[ BIOSITE LOGO ]

May 17, 2007

BY FACSIMILE

Beckman Coulter, Inc.

Louisiana Acquisition Sub, Inc.

4300 N. Harbor Boulevard

P.O. Box 3100

Fullerton, CA 92834-3100 USA

Attention: General Counsel

Facsimile: (714) 773-7936; (714) 773-8543

Re: Termination Notice

Dear Arnie:

Reference is made to that certain Agreement and Plan of Merger dated as of March
24, 2007, among Biosite Incorporated (the “Company”), Beckman Coulter, Inc. and
Louisiana Acquisition Sub, Inc., as amended by that certain Amendment to
Agreement and Plan of Merger dated as of May 1, 2007 (as amended, the “Merger
Agreement”).

This letter constitutes written notice under Section 7.2 of the Merger
Agreement. By delivering this letter, the Company terminates the Merger
Agreement pursuant to Section 7.1(f) thereof. Effective immediately, the Merger
Agreement is terminated and shall be of no further force or effect except as
otherwise provided in Section 7.2 of the Merger Agreement.

 

Very truly yours, Biosite Incorporated By:   /s/ David B. Berger   Name: David
B. Berger   Title: Vice President, Legal Affairs

 

cc: Fred Muto, Esq., Cooley Godward Kronish LLP

     Paul D. Tosetti, Esq., Latham & Watkins LLP

     Cary K. Hyden, Esq., Latham & Watkins LLP

     Jonn R. Beeson, Esq., Latham & Watkins LLP