Mail Stop 6010

Via Facsimile and U.S. Mail


August 2, 2005

Mr. William J. Dawson
Chief Financial Officer
Cerus Corporation
2411 Stanwell Drive
Concord, CA 94520

      Re:	Cerus Corporation
		Form 10-K for Fiscal Year Ended December 31, 2004
	            File No. 000-21937

Dear Mr. Dawson:

      We have limited our review of your filing to the issues we
have
addressed in our comments. In our comments, we ask you to provide
us
with information so we may better understand your disclosure.
After
reviewing this information, we may raise additional comments.

	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.


Financial Statements

Notes to Financial Statements

2. Development and License Agreements, 56-59

1. Please explain in greater detail your accounting policy for
joint
development arrangements.  Specifically please provide the
following
information in disclosure-type format:

* Provide a summary of each joint development arrangement and the
calculation used to determine the net profit or loss.
* Provide to us in a tabular format, the location within the
statement of operations of all revenue that is earned and costs
that
is incurred by you related to the joint development arrangements.
* Provide the authoritative guidance you used to record the profit
or
loss related to the joint development arrangements.

Provide us an analysis of how you considered EITF 99-19 for each
of
your joint development arrangements and the conclusions you
reached.

2. Please explain the reason for deferring the $3.0 million up-
front
payment received in December 2004 from BioOne as a result of
signing
a letter of intent, and indicate the events that will trigger
revenue
recognition and the periods you will recognize revenue.  Please
provide us this information in disclosure-type format.


*    *    *    *

      Please respond to the comment within 10 business days or
tell
us when you will provide us with a response.  Please furnish a
letter
that keys your response to our comment and provides requested
information.  Detailed letters greatly facilitate our review.
Please
file your letter on EDGAR under the form type label CORRESP.

	We urge all persons who are responsible for the accuracy and
adequacy of the disclosure in the filings to be certain that the
filing includes all information required under the Securities and
Exchange Act of 1934 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.

	In connection with responding to our comment, please provide,
in
your letter, a statement from the company acknowledging that

* the company is responsible for the adequacy and accuracy of the
disclosure in the filings;
* staff comments or changes to disclosure in response to staff
comments do not foreclose the Commission from taking any action
with
respect to the filing; and
* the company may not assert staff comments 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 our review of your filing or in
response to our comments on your filing.

      You may contact Todd Sherman, Staff Accountant, at 202-551-
3665
or Kevin Woody, Branch Chief, at 202-551-3629 if you have
questions
regarding the comment.  In this regard, do not hesitate to contact
me, at (202) 551-3679.

							Sincerely,



							Jim B. Rosenberg
						Senior Assistant Chief Accountant
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William J. Dawson
Cerus Corporation
August 2, 2005
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