SECURITIES PURCHASE AGREEMENT This Securities Purchase Agreement (this Agreement ) is dated as of

SECURITIES PURCHASE AGREEMENT

This Securities Purchase Agreement (this

Agreement ) is dated as of August 10, 2012 between Arrowhead Research Corporation, a Delaware corporation (the Company ), and each purchaser identified on the signature pages hereto (each, including its

successors and assigns, a Purchaser and collectively the Purchasers ).

to the terms and conditions set forth in this Agreement and pursuant to an effective registration statement under the Securities Act of 1933, as amended (the Securities Act ), the Company desires to issue and sell to each

Purchaser, and each Purchaser, severally and not jointly, desires to purchase from the Company, securities of the Company as more fully described in this Agreement.

NOW, THEREFORE, IN CONSIDERATION of the mutual covenants contained in this Agreement, and for other good and valuable consideration the receipt and adequacy of which are hereby acknowledged, the Company

and each Purchaser agree as follows:

1.1 Definitions. In addition to the terms defined elsewhere

in this Agreement, for all purposes of this Agreement, the following terms have the meanings set forth in this Section 1.1:

Acquiring Person shall have the meaning ascribed to such term in Section 4.5.

Action shall have the meaning ascribed to such term in Section 3.1(j).

Affiliate means any Person that, directly or indirectly through one or more intermediaries, controls or is controlled by or is under common control with a Person as such terms are used

in and construed under Rule 405 under the Securities Act.

Board of Directors means the

board of directors of the Company.

Business Day means any day except any Saturday, any

Sunday, any day which is a federal legal holiday in the United States or any day on which banking institutions in the State of New York are authorized or required by law or other governmental action to close.

Closing means the closing of the purchase and sale of the Securities pursuant to Section 2.1.

Closing Date means the Trading Day on which all of the Transaction Documents have been

executed and delivered by the applicable parties thereto, and all conditions precedent to (i) the Purchasers obligations to pay the Subscription Amount and (ii) the Company s obligations to deliver the Securities, in each case,

have been satisfied or waived, but in no event later than the third Trading Day following the date hereof.

Commission means the United States Securities and

Exchange Commission.

Common Stock means the common stock of the Company, par value $0.001

per share, and any other class of securities into which such securities may hereafter be reclassified or changed.

Common Stock Equivalents means any securities of the Company or the Subsidiaries which would entitle the holder thereof to acquire at any time Common Stock, including, without

limitation, any debt, preferred stock, right, option, warrant or other instrument that is at any time convertible into or exercisable or exchangeable for, or otherwise entitles the holder thereof to receive, Common Stock.

Company Counsel means Ropes & Gray, LLP.

Disclosure Schedules means the Disclosure Schedules of the Company delivered concurrently herewith.

EGS means Ellenoff Grossman & Schole LLP, with offices located at 150 East 42nd

Street, New York, New York 10017.

Escrow Agent means Signature Bank, a New York State

chartered bank, with offices at 261 Madison Avenue, New York, New York 10016.

Agreement means the escrow agreement entered into prior to the date hereof, by and among the Company, the Escrow Agent and Rodman & Renshaw, LLC pursuant to which the Purchasers shall deposit Subscription Amounts with the Escrow

Agent to be applied to the transactions contemplated hereunder.

Evaluation Date shall have

the meaning ascribed to such term in Section 3.1(r).

Exchange Act means the Securities

Exchange Act of 1934, as amended, and the rules and regulations promulgated thereunder.

Issuance means the issuance of (a) shares of Common Stock or options to employees, officers, consultants or directors of the Company pursuant to any stock or option plan duly adopted for such purpose, by a majority of the non-employee

members of the Board of Directors or a majority of the members of a committee of non-employee directors established for such purpose, (b) securities upon the exercise or exchange of or conversion of any Securities issued hereunder and/or other

securities exercisable or exchangeable for or convertible into shares of Common Stock issued and outstanding on the date of this Agreement, provided that such securities have not been amended since the date of this Agreement to increase the number

of such securities or to decrease the exercise price, exchange price or conversion price of such securities (except for any price adjustments made in accordance with the terms of any such securities, which adjustments have been disclosed in the SEC

Reports), (c) shares of Common Stock or Common Stock Equivalents issued pursuant to any commitments of the Company existing as of the date of this Agreement and as set forth in the Prospectus Supplement (excluding, for the avoidance of doubt,

issuances under the Lincoln park Capital Facility, which shall not be

deemed an Exempt Issuance) and (d) securities issued pursuant to acquisitions or strategic transactions approved by a majority of the disinterested directors of the Company (including

transactions entered into prior to the date hereof), provided that any such issuance shall only be to a Person (or to the equity holders of a Person) which is, itself or through its subsidiaries, an operating company or an owner of an asset in a

business synergistic with the business of the Company and shall provide to the Company additional benefits in addition to the investment of funds, but shall not include a transaction in which the Company is issuing securities primarily for the

purpose of raising capital or to an entity whose primary business is investing in securities.

FCPA means the Foreign Corrupt Practices Act of 1977, as amended.

FDA shall have the meaning ascribed to such term in Section 3.1(gg).

FDCA shall have the meaning ascribed to such term in Section 3.1(gg).

GAAP shall have the meaning ascribed to such term in Section 3.1(h).

Indebtedness shall have the meaning ascribed to such term in Section 3.1(z).

Intellectual Property Rights shall have the meaning ascribed to such term in Section 3.1(o).

Liens means a lien, charge, pledge, security interest, encumbrance, right of first refusal,

preemptive right or other restriction.

Material Adverse Effect shall have the meaning

assigned to such term in Section 3.1(b).

Material Permits shall have the meaning

ascribed to such term in Section 3.1(m).

Participation Maximum shall have the meaning

ascribed to such term in Section 4.11(a).

Per Share Purchase Price equals $2.76,

subject to adjustment for reverse and forward stock splits, stock dividends, stock combinations and other similar transactions of the Common Stock that occur after the date of this Agreement.

Person means an individual or corporation, partnership, trust, incorporated or unincorporated

association, joint venture, limited liability company, joint stock company, government (or an agency or subdivision thereof) or other entity of any kind.

Pharmaceutical Product shall have the meaning ascribed to such term in Section 3.1(gg).

Proceeding means an action, claim, suit, investigation or

proceeding (including, without limitation, an informal investigation or partial proceeding, such as a deposition), whether commenced or threatened.

Prospectus means the final prospectus filed for the Registration Statement.

Prospectus Supplement means the supplement to the Prospectus complying with Rule 424(b) of the Securities Act that is filed with the Commission and delivered by the Company to each

Purchaser at the Closing.

Purchaser Party shall have the meaning ascribed to such term in

Registration Statement means the effective registration statement with

Commission file No. 333-176159 which registers the sale of the Shares, the Warrants and the Warrant Shares to the Purchasers.

Required Approvals shall have the meaning ascribed to such term in Section 3.1(e).

Rule 144 means Rule 144 promulgated by the Commission pursuant to the Securities Act, as such Rule may be amended or interpreted from time to time, or any similar rule or regulation

hereafter adopted by the Commission having substantially the same purpose and effect as such Rule.

Rule 424 means Rule 424 promulgated by the Commission pursuant to the Securities Act, as such Rule may

be amended or interpreted from time to time, or any similar rule or regulation hereafter adopted by the Commission having substantially the same purpose and effect as such Rule.

SEC Reports shall have the meaning ascribed to such term in Section 3.1(h).

Securities means the Shares, the Warrants and the Warrant Shares.

Securities Act means the Securities Act of 1933, as amended, and the rules and regulations promulgated

Shares means the shares of Common Stock issued or issuable to each Purchaser

pursuant to this Agreement.

Short Sales means all short sales as defined in

Rule 200 of Regulation SHO under the Exchange Act (but shall not be deemed to include the location and/or reservation of borrowable shares of Common Stock).

Subscription Amount means, as to each Purchaser, the aggregate amount to be paid for Shares and Warrants purchased hereunder as specified below such Purchaser s name on the

signature page of this Agreement and next to the heading Subscription Amount, in United States dollars and in immediately available funds.

Subsidiary means any subsidiary of the Company as set

forth on Schedule 3.1(a), and shall, where applicable, also include any direct or indirect subsidiary of the Company formed or acquired after the date hereof.

Trading Day means a day on which the principal Trading Market is open for trading.

Trading Market means any of the following markets or exchanges on which the Common Stock is listed or

quoted for trading on the date in question: the NYSE MKT, the Nasdaq Capital Market, the Nasdaq Global Market, the Nasdaq Global Select Market, the New York Stock Exchange or the OTC Bulletin Board (or any successors to any of the foregoing).

Transaction Documents means this Agreement, the Warrants and any other documents or

agreements executed in connection with the transactions contemplated hereunder.

Agent means Computershare Limited, the current transfer agent of the Company, with a mailing address of 330 North Brand Boulevard, Suite 701, Glendale, CA 91203-2149 and a facsimile number of (818) 502-0674, and any successor transfer

agent of the Company.