Mail Stop 6010

									March 20, 2006

Dr. Leon Ekchian, President
Arrowhead Research Corporation
201 South Lake Avenue - Suite 703
Pasadena, California  91101


Re:  	Arrowhead Research Corporation
Form S-3 Registration Statement
Filed March 9, 2006
	File No. 333-132310


Dear Dr. Ekchian:

      We have limited our review of your filing to the issues we
have
addressed in our comments.  Where indicated, we think you should
revise your document in response to these comments.  If you
disagree,
we will consider your explanation as to why our comment is
inapplicable or a revision is unnecessary.  Please be as detailed
as
necessary in your explanation.  In some of our comments, we may
ask
you to provide us with information so we may better understand
your
disclosure.  After reviewing this information, we may raise
additional comments.  After our comments have been satisfied, we
will
consider your request for acceleration of the effective date of
the
registration statement.

      Please understand that the purpose of our review process is
to
assist you in your compliance with the applicable disclosure
requirements and to enhance the overall disclosure in your filing.
We look forward to working with you in these respects.  We welcome
any questions you may have about our comments or any other aspect
of
our review.  Feel free to call us at the telephone numbers listed
at
the end of this letter.

Comments

1. Please revise the signature page of your registration statement
to
identify and include the signature of your principal accounting
officer/controller.


      As appropriate, please amend your registration statement in
response to these comments.  You may wish to provide us with
marked
copies of the amendment to expedite our review.  Please furnish a
cover letter with your amendment that keys your responses to our
comments and provides any requested information.  Detailed cover
letters greatly facilitate our review.  Please understand that we
may
have additional comments after reviewing your amendment and
responses
to our comments.

      We urge all persons who are responsible for the accuracy and
adequacy of the disclosure in the filing to be certain that the
filing includes all information required under the Securities Act
of
1933 and that they have provided all information investors require
for an informed investment decision.  Since the company and its
management are in possession of all facts relating to a company`s
disclosure, they are responsible for the accuracy and adequacy of
the
disclosures they have made.

      Notwithstanding our comments, in the event the company
requests
acceleration of the effective date of the pending registration
statement, it should furnish a letter, at the time of such
request,
acknowledging that:

?	should the Commission or the staff, acting pursuant to
delegated
authority, declare the filing effective, it does not foreclose the
Commission from taking any action with respect to the filing;

?	the action of the Commission or the staff, acting pursuant to
delegated authority, in declaring the filing effective, does not
relieve the company from its full responsibility for the adequacy
and
accuracy of the disclosure in the filing; and

?	the company may not assert staff comments and the declaration
of
effectiveness as a defense in any proceeding initiated by the
Commission or any person under the federal securities laws of the
United States.

	In addition, please be advised that the Division of
Enforcement
has access to all information you provide to the staff of the
Division of Corporation Finance in connection with our review of
your
filing or in response to our comments on your filing.

      We will consider a written request for acceleration of the
effective date of the registration statement as confirmation of
the
fact that those requesting acceleration are aware of their
respective
responsibilities under the Securities Act of 1933 and the
Securities
Exchange Act of 1934 as they relate to the proposed public
offering
of the securities specified in the above registration statement.
We
will act on the request and, pursuant to delegated authority,
grant
acceleration of the effective date.

      We direct your attention to Rules 460 and 461 regarding
requesting acceleration of a registration statement.  Please allow
adequate time after the filing of any amendment for further review
before submitting a request for acceleration.  Please provide this
request at least two business days in advance of the requested
effective date.

      Please contact Mary K. Fraser at (202) 551-3609 or me at
(202)
551-3710 with any other questions.

      					Sincerely,



      					Jeffrey Riedler
      Assistant Director


Cc:  	Rachael Simonoff Wexler, Esq.
	Alschuler Grossman Stein & Kahan LLP
	1620 26th St. - North Tower, Fourth Floor
	Santa Monica, CA  90404
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Nicholas J. Rossettos
Manhattan Pharmaceuticals, Inc.
February 23, 2006
Page 3