COMBIMATRIX NUMBER CBMX THIS CERTIFICATE IS TRANSFERABLE IN CANTON, MA, NEW YORK, NY, JERSEY CITY, NJ, AND PITTSBURGH, PA SHARES CUSIP 20009T 30 3 SEE REVERSE FOR CERTAIN DEFINITIONS INCORPORATED UNDER THE LAWS OF THE STATE OF DELAWARE This certifies that SPECIMEN COUNTERSIGNED AND REGISTERED: COMPUTERSHARE SHAREOWNER SERVICES LLC TRANSFER AGENT AND REGISTRAR BY: AUTHORIZED SIGNATURE is the record holder of FULLY PAID AND NONASSESSABLE SHARES OF COMMON STOCK, $0.001 PAR VALUE, OF COMBIMATRIX CORPORATION transferable on the books of the corporation 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: DELAWARE SEAL COMBIMATRIX CORPORATION2002 CHIEF FINANCIAL OFFICER AND SECRETARY PRESIDENT & CHIEF EXECUTIVE OFFICER

A statement of the rights, preferences, privileges and restrictions granted to or imposed upon the respective classes or series of shares of stock of the Corporation and upon holders thereof as established by the Certificate of Incorporation or by any Certificate of Designation of Preferred Stock, and the number of shares constituting each series and the designations thereof, may be obtained by any shareholder upon request and without charge at the principal office of the corporation. 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 COM PROP – as community property 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(s), assign(s) and transfer(s) unto 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 capital stock represented by within Certificate, and do hereby irrevocably constitute and appoint attorney-in-fact to transfer the said stock on the books of the within named Corporation with full power of the substitution in the premises. Dated X X NOTICE: THE SIGNATURE TO THIS ASSIGNMENT MUST CORRESPOND WITH THE NAME AS WRITTEN UPON THE FACE OF THE CERTIFICATE IN EVERY PARTICULAR, WITHOUT ALTERATION OR ENLARGEMENT OR ANY CHANGE WHATSOEVER. Signature(s) Guaranteed: By 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. GUARANTEES BY A NOTARY PUBLIC ARE NOT ACCEPTABLE. SIGNATURE GUARANTEES MUST NOT BE DATED.