Sec Form 13G Filing - Knott David M filing for ARROWHEAD PHARMACEUTICALS INC. (ARWR) - 2008-02-13

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13G

o

Rule 13d-1(b)

x

Rule 13d-1(c)

o

Rule 13d-1(d)

CUSIP No. 042797100

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
David M. Knott

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

o

(b)

x

3.

SEC Use Only

4.

Citizenship or Place of Organization
United States of America

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
338,543

6.

Shared Voting Power
15,150

7.

Sole Dispositive Power
357,143

8.

Shared Dispositive Power
0

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
357,143

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o

11.

Percent of Class Represented by Amount in Row (9)
0.9%

12.

Type of Reporting Person (See Instructions)
IN

CUSIP No. 042797100

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
Dorset Management Corporation

11-2873658

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

o

(b)

x

3.

SEC Use Only

4.

Citizenship or Place of Organization
United States of America

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
338,543

6.

Shared Voting Power
15,150

7.

Sole Dispositive Power
357,143

8.

Shared Dispositive Power
0

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
357,143

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o

11.

Percent of Class Represented by Amount in Row (9)
0.9%

12.

Type of Reporting Person (See Instructions)
CO

CUSIP No. 565756202

1.

Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
Knott Partners Offshore Master Fund, L.P.

2.

Check the Appropriate Box if a Member of a Group (See Instructions)

(a)

o

(b)

x

3.

SEC Use Only

4.

Citizenship or Place of Organization
Cayman Islands

Number of
Shares
Beneficially
Owned by
Each
Reporting
Person With

5.

Sole Voting Power
161,668

6.

Shared Voting Power
0

7.

Sole Dispositive Power
161,668

8.

Shared Dispositive Power
0

9.

Aggregate Amount Beneficially Owned by Each Reporting Person
161,668

10.

Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)  o

11.

Percent of Class Represented by Amount in Row (9)
0.4%

12.

Type of Reporting Person (See Instructions)
PN

Item 1.

(a)

Name of Issuer
Arrowhead Research Corporation (the “Company”)

(b)

Address of Issuer’s Principal Executive Offices
201 S. Lake Avenue

Pasadena, California  911061

Item 2.

(a)

Name of Person Filing
David M. Knott; Dorset Management Corporation; Knott Partners Offshore Master Fund, L.P.

(b)

Address of Principal Business Office or, if none, Residence
For David M. Knott and Dorset Management Corporation

485 Underhill Boulevard, Suite 205

Syosset, New York 11791

For Knott Partners Offshore Master Fund, L.P.:

InterCaribbean Services Limited c/o CITCO Fund Services (Curacao)

N.V., Kaya Flamboyan 9, Curacao, Netherlands Antilles

Attention: Sharin Lasten

(c)

Citizenship
David M. Knott - United States of America;

Dorset Management Corporation – New York

Knott Partners Offshore Master Fund, L.P. – Cayman Islands

(d)

Title of Class of Securities
Common Stock $0.001 Par Value

(e)

CUSIP Number
042797100

Item 3.

If this statement is filed pursuant to §§240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:

(a)

o

Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o).

(b)

o

Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c).

(c)

o

Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c).

(d)

o

Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C 80a-8).

(e)

o

An investment adviser in accordance with §240.13d-1(b)(1)(ii)(E);

(f)

o

An employee benefit plan or endowment fund in accordance with §240.13d-1(b)(1)(ii)(F);

(g)

o

A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);

(h)

o

A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);

(i)

o

A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);

(j)

o

Group, in accordance with §240.13d-1(b)(1)(ii)(J).

Item 4.

Ownership

Provide the following information regarding the aggregate number and percentage of the class of securities of the issuer identified in Item 1.

(a)

Amount beneficially owned:   

(b)

Percent of class:   

(c)

Number of shares as to which the person has:

(i)

Sole power to vote or to direct the vote   

(ii)

Shared power to vote or to direct the vote    

(iii)

Sole power to dispose or to direct the disposition of   

(iv)

Shared power to dispose or to direct the disposition of   

David M. Knott; Dorset Management Corporation; Knott Partners Offshore Master Fund, L.P.

See Rows 5 through 9 and 11 on  pages 2, 3 and 4.

As of the date of this filing, each Reporting Person may be deemed to be the beneficial owner of the number of currently exercisable warrants (the “Warrants”) for the purchase of the number of shares of Common Stock of the Company, set forth on Row 9 of the corresponding Cover Page of this Schedule 13G for such Reporting Person. Each Warrant entitles the holder to purchase one share of the Company’s Common Stock at a price of $4.50.  Each Warrant will expire on January 24, 2011, or earlier upon redemption. 

Item 5.

Ownership of Five Percent or Less of a Class

If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following   x.

This statement is being filed to report the fact that as of the date hereof the following Reporting Persons have ceased to be the beneficial owner of more than five percent of the class of securities, as reported on Rows 5 through 9 and 11 on pages 2-3: David M. Knott and Dorset Management Corporation

Item 6.

Ownership of More than Five Percent on Behalf of Another Person

N/A

Item 7.

Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on By the Parent Holding Company or Control Person

N/A

Item 8.

Identification and Classification of Members of the Group

N/A

Item 9.

Notice of Dissolution of Group

N/A

Item 10.

Certification

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect.

February 13, 2008

Date

/s/ David M. Knott

Signature

DORSET MANAGEMENT CORPORATION

By:

   /s/ David M. Knott

David M. Knott, President

KNOTT PARTNERS OFFSHORE MASTER

FUND, L.P.

By:

Knott Partners Management, LLC,

General Partner

By:

   /s/ David M. Knott

Name:

David M. Knott

Title:

Managing Member