FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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(Print or Type Responses)

1. Name and Address of Reporting Person * KNOTT DAVID M   2. Issuer Name and Ticker or Trading Symbol ARROWHEAD RESEARCH CORP [ARWR] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director __X__ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 485 UNDERHILL BLVD, STE 205 3. Date of Earliest Transaction (Month/Day/Year) 03/21/2007 (Street) SYOSSET, NY 11791-3419 4. If Amendment, Date Original Filed(Month/Day/Year) 6. Individual or Joint/Group Filing(Check Applicable Line) _X_ Form filed by One Reporting Person ___ Form filed by More than One Reporting Person (City) (State) (Zip) Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned

1.Title of Security (Instr. 3) 2. Transaction Date (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 03/21/2007   S   24,200 D $ 3.8084 728,600 I By Shoshone Partners, L.P. (1) (3) Common Stock               4,300 I By Mulsanne Partners, L.P. (1) (3) Common Stock 03/21/2007   S   49,400 D $ 3.8084 1,764,231 I By Knott Partners Offshore Master Fund, L.P. (1) (3) Common Stock 03/21/2007   S   7,800 D $ 3.8084 241,578 I By Managed Accounts (2) (3) Common Stock 03/21/2007   S   52,300 D $ 3.8084 1,241,800 I By Knott Partners, L.P. (1) (3) Common Stock 03/21/2007   S   21,200 D $ 3.8197 707,400 I By Shoshone Partners, L.P. (1) (3) Common Stock 03/21/2007   S   43,450 D $ 3.8197 1,720,781 I By Knott Partners Offshore Master Fund, L.P. (1) (3) Common Stock 03/21/2007   S   6,800 D $ 3.8197 234,778 I By Managed Accounts (2) (3) Common Stock 03/21/2007   S   45,800 D $ 3.8197 1,196,000 I By Knott Partners, L.P. (1) (3) Common Stock 03/21/2007   S   210,100 D $ 3.8 497,300 I By Shoshone Partners, L.P. (1) (3) Common Stock 03/21/2007   S   428,500 D $ 3.8 1,292,281 I By Knott Partners Offshore Master Fund, L.P. (1) (3) Common Stock 03/21/2007   S   68,000 D $ 3.8 166,778 I By Managed Accounts (2) (3) Common Stock 03/21/2007   S   453,400 D $ 3.8 742,600 I By Knott Partners, L.P. (1) (3)

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Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)

1. Title of Derivative Security (Instr. 3)

2. Conversion or Exercise Price of Derivative Security

3. Transaction Date (Month/Day/Year)

3A. Deemed Execution Date, if any (Month/Day/Year)

4. Transaction Code (Instr. 8)

5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5)

6. Date Exercisable and Expiration Date (Month/Day/Year)

7. Title and Amount of Underlying Securities (Instr. 3 and 4)

8. Price of Derivative Security (Instr. 5)

9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)

10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4)

11. Nature of Indirect Beneficial Ownership (Instr. 4)

Code

V

(A)

(D)

Date Exercisable

Expiration Date

Title

Amount or Number of Shares

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
KNOTT DAVID M 485 UNDERHILL BLVD STE 205 SYOSSET, NY 11791-3419		X

Signatures

/s/ David M. Knott		03/22/2007
**Signature of Reporting Person		Date

Explanation of Responses:

*	If the form is filed by more than one reporting person, see Instruction 4(b)(v).
**	Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1)	The Reporting Person is the managing member of Knott Partners Management, LLC, which is (i) the sole general partner of Shoshone Partners, L.P., Knott Partners Offshore Master Fund, L.P. and Mulsanne Partners, L.P., and (ii) the managing general partner of Knott Partners, L.P. The Reporting Person is also a general partner of Knott Partners, L.P.
(2)	The entry represents securities of the issuer held by managed accounts for which Dorset Management Corporation provides investment management services (the "Managed Accounts").
(3)	As a result of the Reporting Person's interests in Knott Partners Management, LLC and in Dorset Management Corporation, the Reporting Person has investment discretion and control of the securities represented in this entry. The Reporting Person may be deemed to beneficially own an indirect pecuniary interest in the securities represented in this entry as a result of its performance-related fee. Except with respect to Shoshone Partners, L.P. and Knott Partners, L.P., in which the Reporting Person owns a beneficial interest, the Reporting Person disclaims beneficial ownership therein except to the extent ultimately realized. Each of Shoshone Partners, L.P., Mulsanne Partners, L.P., Knott Partners Offshore Master Fund, L.P., Knott Partners, L.P. and the Managed Accounts disclaims beneficial ownership of securities reported as owned by any other party.

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