Exhibit 10.4

FORM OF LOCK-UP AGREEMENT

September 28, 2012

Each Purchaser referenced below:

Re:                             Securities Purchase Agreement, dated as of September 28, 2012 (the “Purchase Agreement”), between Combimatrix Corporation, a Delaware corporation (the “Company”) and the purchasers signatory thereto (each, a “Purchaser” and, collectively, the “Purchasers”)

Ladies and Gentlemen:

Defined terms not otherwise defined in this letter agreement (the “Letter Agreement”) shall have the meanings set forth in the Purchase Agreement.  Pursuant to Section 2.2 of the Purchase Agreement and in satisfaction of a condition of the Company’s obligations under the Purchase Agreement, the undersigned irrevocably agrees with the Company that, from the date hereof until the 180th day following the earlier of the date that (a) all of the Conversion Shares are registered for resale pursuant to one or more Registration Statements or (b) all of the Conversion Shares may be resold pursuant to Rule 144 (as to non-Affiliates, without volume or manner restrictions) (such period, the “Restriction Period”, which period shall be tolled for any periods during such period that either a Registration Statement or Rule 144 is not available for the resale of all of the then outstanding or issuable Conversion Shares), the undersigned will not offer, sell,  contract to sell, hypothecate, pledge or otherwise dispose of (or enter into any transaction which is designed to, or might reasonably be expected to, result in the disposition (whether by actual disposition or effective economic disposition due to cash settlement or otherwise) by the undersigned or any Affiliate of the undersigned or any person in privity with the undersigned or any Affiliate of the undersigned), directly or indirectly, including the filing (or participation in the filing) of a registration statement with the Commission in respect of, or establish or increase a put equivalent position or liquidate or decrease a call equivalent position within the meaning of Section 16 of the Exchange Act with respect to, any shares of Common Stock or Common Stock Equivalents beneficially owned, held or hereafter acquired by the undersigned (the “Securities”).  Beneficial ownership shall be calculated in accordance with Section 13(d) of the Exchange Act.  In order to enforce this covenant, the Company shall impose irrevocable stop-transfer instructions preventing the Transfer Agent from effecting any actions in violation of this Letter Agreement.

Notwithstanding the foregoing, the undersigned may transfer Securities during the Restriction Period in the following transactions: (i) as a bona fide gift or gifts; (ii) to any trust for the direct or indirect benefit of the undersigned or the immediate family of the undersigned, or by any trust to its beneficiaries; (iii) as a distribution to members, partners or stockholders of the undersigned; (iv) to the undersigned’s Affiliates or to any investment fund or other entity controlled or managed by the undersigned; (v) to any beneficiary of the undersigned pursuant to a will or other testamentary document or applicable laws of descent; or (vi) to any corporation, partnership, limited liability company or other entity all of the beneficial ownership interests of which are held by the undersigned or immediate family of the undersigned; provided that each such donee, trustee, distributee, or transferee, as the case may be, agrees to be bound by this Letter Agreement.

For purposes of this Letter Agreement, “immediate family” shall mean any relationship by blood, marriage or adoption, not more remote than first cousin.

The undersigned acknowledges that the execution, delivery and performance of this Letter Agreement is a material inducement to each Purchaser to complete the transactions contemplated by the Purchase Agreement and that each Purchaser (which shall be a third party beneficiary of this Letter Agreement) and the Company shall be entitled to specific performance of the undersigned’s obligations hereunder.  The undersigned hereby represents that the undersigned has the power and authority to execute, deliver and perform this Letter Agreement, that the undersigned has received adequate consideration therefor and that the undersigned will indirectly benefit from the closing of the transactions contemplated by the Purchase Agreement.

This Letter Agreement may not be amended or otherwise modified in any respect without the written consent of each of the Company, each Purchaser and the undersigned.  This Letter Agreement shall be construed and enforced in accordance with the laws of the State of New York without regard to the principles of conflict of laws. The undersigned hereby irrevocably submits to the exclusive jurisdiction of the United States District Court sitting in the Southern District of New York and the courts of the State of New York located in Manhattan, for the purposes of any suit, action or proceeding arising out of or relating to this Letter Agreement, and hereby waives, and agrees not to assert in any such suit, action or proceeding, any claim that (i) it is not personally subject to the jurisdiction of such court, (ii) the suit, action or proceeding is brought in an inconvenient forum, or (iii) the venue of the suit, action or proceeding is improper. The undersigned hereby irrevocably waives personal service of process and consents to process being served in any such suit, action or proceeding by receiving a copy thereof sent to the Company at the address in effect for notices to it under the Purchase Agreement and agrees that such service shall constitute good and sufficient service of process and notice thereof.  The undersigned hereby waives any right to a trial by jury.  Nothing contained herein shall be deemed to limit in any way any right to serve process in any manner permitted by law.  The undersigned agrees and understands that this Letter Agreement does not intend to create any relationship between the undersigned and each Purchaser and that each Purchaser is not entitled to cast any votes on the matters herein contemplated and that no issuance or sale of the Securities is created or intended by virtue of this Letter Agreement.

By its signature below, the Transfer Agent hereby acknowledges and agrees that, reflecting this Letter Agreement, it has placed an irrevocable stop transfer instruction on all Securities registered in the name of the undersigned until the end of the Restriction Period.  This Letter Agreement shall be binding on successors and assigns of the undersigned with respect to the Securities and any such successor or assign shall enter into a similar agreement for the benefit of the Purchasers.

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This Letter Agreement may be executed in two or more counterparts, all of which when taken together may be considered one and the same agreement.

Address for Notice:

Number of shares of Common Stock

Number of shares of Common Stock underlying subject to warrants, options, debentures or other convertible securities

By signing below, the Company agrees to enforce the restrictions on transfer set forth in this Letter Agreement.

COMBIMATRIX CORPORATION

Acknowledged and agreed to

as of the date set forth above:

COMPUTERSHARE

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