Common Stock Certificate and Rights Agreement Reference for Biosite Incorporated

Exhibit 4.1

[FACE OF CERTIFICATE]

[LOGO]

NUMBER
BST

SHARES

INCORPORATED UNDER THE LAWS OF THE STATE OF DELAWARE

THIS CERTIFICATE IS TRANSFERABLE IN THE CITY OF BOSTON, MA OR NEW YORK, NY

SEE REVERSE FOR CERTAIN DEFINITIONS AND A STATEMENT AS TO RIGHTS, PREFERENCES, PRIVILEGES AND RESTRICTIONS, IF ANY

CUSIP 090945 10 6

This Certifies that

is the record holder of

FULLY PAID AND NONASSESSABLE SHARES OF COMMON STOCK, $.01 PAR VALUE PER SHARE, OF

BIOSITE INCORPORATED

transferable on the books of the Corporation by the holder hereof in person or by duly authorized Attorney upon surrender of this certificate properly endorsed. This certificate is not valid until countersigned by the Transfer Agent and registered by the Registrar. WITNESS the facsimile seal of the Corporation and the facsimile signatures of its duly authorized officers.

Dated

VICE PRESIDENT, FINANCE AND CHIEF FINANCIAL OFFICER

PRESIDENT AND CHIEF EXECUTIVE OFFICER

COUNTERSIGNED AND REGISTERED: AMERICAN STOCK TRANSFER & TRUST COMPANY TRANSFER AGENT AND REGISTRAR

[BACK OF CERTIFICATE]

A statement of the powers, designations, preferences and relative, participating, optional or other special rights of each class of stock or series thereof and the qualifications, limitations or restrictions of such preferences and/or rights as established, from time to time, by the Certificate of Incorporation of the Corporation and by any certificate of determination, the number of shares constituting each class and series, and the designations thereof, may be obtained by the holder hereof upon request and without charge at the principal office of the Corporation.

This certificate also evidences and entitles the holder hereof to certain Rights as set forth in a Rights Agreement between Biosite Incorporated (the “Company”) and American Stock Transfer & Trust Company (the “Rights Agent”) dated as of March 1, 2000, as amended from time to time (the “Rights Agreement”), the terms of which are hereby incorporated herein by reference and a copy of which is on file at the principal offices of the Company. Under certain circumstances, as set forth in the Rights Agreement, such Rights may be redeemed, may expire or may be evidenced by separate Certificates and will no longer be evidenced by this Certificate. The Company will mail to the holder of this certificate a copy of the Rights Agreement without charge within five days after receipt of a written request therefor. Under certain circumstances, Rights issued to Acquiring Person (as defined in the Rights Agreement) or certain related Persons and any subsequent holder of such Rights may become null and void.

The following abbreviations, when used in the inscription on the face of this certificate, shall be construed as though they were written out in full according to applicable laws or regulations:

TEN COM — as tenants in common TEN ENT — as tenants by the entireties JT TEN — as joint tenants with right of survivorship and not as tenants in common

UNIF GIFT MIN ACT —                                Custodian

                                                   (Cust) (Minor) under Uniform Gifts to Minors Act
(State)
UNIF TRF MIN ACT —                  Custodian (until age                 )
(Cust)
under Uniform Transfers (Minor) to Minors Act
(State)

Additional abbreviations may also be used though not in the above list.

FOR VALUE RECEIVED, hereby sell, assign and transfer unto

2

PLEASE INSERT SOCIAL SECURITY OR OTHER IDENTIFYING NUMBER OF ASSIGNEE

(PLEASE PRINT OR TYPEWRITE NAME AND ADDRESS, INCLUDING ZIP CODE, OF ASSIGNEE)

Shares of the common stock represented by the within Certificate, and do hereby irrevocably constitute and appoint                               

Attorney to transfer the said stock on the books of the within named Corporation with full power of substitution in the premises. Dated

NOTICE: THE SIGNATURE(S) TO THIS ASSIGNMENT MUST CORRESPOND WITH THE NAME(S) AS WRITTEN UPON THE FACE OF THE CERTIFICATE IN EVERY PARTICULAR, WITHOUT ALTERATION OR ENLARGEMENT OR ANY CHANGE WHATEVER.

Signature (s) Guaranteed

THE SIGNATURE(S) SHOULD BE GUARANTEED BY AN ELIGIBLE GUARANTOR INSTITUTION (BANKS, STOCKBROKERS, SAVINGS AND LOAN ASSOCIATIONS AND CREDIT UNIONS WITH MEMBERSHIP IN AN APPROVED SIGNATURE GUARANTEE MEDALLION PROGRAM), PURSUANT TO S.E.C. RULE 17Ad-15.

3