UNITED STATES
SECURITIES AND EXCHANGE COMMISSIONWashington, D.C. 20549

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FORM 10-Q/A
Amendment No. 1

(Mark One)

|ý | ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934
|- | ------------------------------------------------------------------------------------

For the quarterly period ended September 30, 2004

OR

|o | TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934
|- | ----------------------------------------------------------------------------------------

For the transition period from  to

Commission file number 0-12798

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CHIRON CORPORATION(Exact name of registrant as specified in its charter)

Delaware(State or other jurisdiction of
incorporation or organization)

94-2754624(I.R.S. Employer Identification No.)4560 Horton Street, Emeryville, California(Address of principal executive offices)

94608(Zip code)(510) 655-8730(Registrant's telephone number, including area code)Not Applicable(Former name, former address and former fiscal year, if changed since last report)


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Indicate
by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the
preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.

Yes ý        No o

Indicate by check mark whether the registrant is an accelerated filer (as defined in Rule 12b-2 of the Exchange Act).

Yes ý        No o

Indicate
the number of shares outstanding of each of the issuer's classes of common stock, as of the latest practicable date.

|Title of Class                |  | Outstanding at November 30, 2004
|----------------------------- |  | --------------------------------
|Common Stock, $0.01 par value |  | 186,848,090                     



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PART II. OTHER INFORMATION

Item 6. Exhibits



|Exhibit
Number |  | Exhibit                                                                                                                                                                                                                                                                                                                          
|-------------- |  | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|3.01           |  | Restated Certificate of Incorporation of Chiron, as filed with the Office of the Secretary of State of Delaware on August 17, 1987, incorporated by reference to Exhibit 3.01 of Chiron's report on Form 10-K for fiscal year
1996.                                                                                              
|3.02           |  | Certificate of Amendment of Restated Certificate of Incorporation of Chiron, as filed with the Office of the Secretary of State of Delaware on December 12, 1991, incorporated by reference to Exhibit 3.02 of Chiron's report on Form 10-K
for fiscal year 1996.                                                                
|3.03           |  | Certificate of Amendment of Restated Certificate of Incorporation of Chiron, as filed with the Office of the Secretary of State of Delaware on May 22, 1996, incorporated by reference to Exhibit 3.04 of Chiron's report on Form 10-Q for
the period ended June 30, 1996.                                                       
|3.04           |  | Bylaws of Chiron, as amended and restated, incorporated by reference to Exhibit 3.04 of Chiron's report on Form 10-K for fiscal year 2003.                                                                                                                                                                                       
|4.01           |  | Indenture between Chiron and State Street Bank and Trust Company, dated as of June 12, 2001, incorporated by reference to Exhibit 4.01 of Chiron's report on Form 10-Q for the period ended June 30, 2001.                                                                                                                       
|4.02           |  | Registration Rights Agreement between Chiron and Merrill Lynch & Co., Inc., and Merrill Lynch, Pierce, Fenner & Smith, Incorporated, incorporated by reference to Exhibit 4.02 of Chiron's report on Form 10-Q for the period
ended June 30, 2001.                                                                               
|4.03           |  | Form of Liquid Yield Option Note due 2031 (Zero CouponSenior) (included as exhibits A-1 and A-2 to the Indenture filed as Exhibit 4.01 to Chiron's report on Form 10-Q for the period ended June 30, 2001),
incorporated by reference to Exhibit 4.03 of Chiron's report on Form 10-Q for the period ended June 30, 2001.      
|4.04           |  | Indenture between Chiron and U.S. Bank National Association, as trustee, dated as of July 30, 2003, incorporated by reference to Exhibit 4.1 of Chiron's registration statement on Form S-3 filed with the Commission on September 23,
2003.                                                                                     
|4.05           |  | Registration Rights Agreement dated as of July 30, 2003, between Chiron and Morgan Stanley & Co., Goldman, Sachs & Co., Banc of America Securities LLC and BNP Paribas Securities Corp., incorporated by reference to
Exhibit 4.3 of Chiron's registration statement on Form S-3 filed with the Commission on September 23, 2003.
|4.06           |  | Form of Convertible Debentures (included in Exhibit 4.04), incorporated by reference to Exhibit 4.2 of Chiron's registration statement on Form S-3 filed with the Commission on September 23, 2003.                                                                                                                              
|4.07           |  | Indenture between Chiron and U.S. Bank National Association, as trustee, dated as of June 22, 2004, incorporated by reference to Exhibit 4.07 of Chiron's report on Form 10-Q for the period ended June 30, 2004.                                                                                                                
|4.08           |  | Registration Rights Agreement dated as of June 22, 2004, between Chiron, Credit Suisse First Boston, LLC and Morgan Stanley & Co., Goldman, Sachs & Co., Incorporated, incorporated by reference to Exhibit 4.08 of Chiron's
report on Form 10-Q for the period ended June 30, 2004.                                             
|               |  |                                                                                                                                                                                                                                                                                                                                  

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|4.09   |  | Specimen of Convertible Debentures (included as Exhibit A to the Indenture referenced as Exhibit 4.07 of Chiron's report on Form 10-Q for June 30, 2004) issued on June 22, 2004, incorporated by reference to Exhibit 4.09
of Chiron's report on Form 10-Q for the period ended June 30, 2004.                                                                                                     
|------ |  | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|10.102 |  | Amended and Restated Revolving Credit Agreement, dated as of August 13, 2002, by and between Chiron and Bank of America, N.A., and exhibits thereto, incorporated by reference to Exhibit 10.102 of Chiron's report on Form 10-Q for
September 30, 2002.                                                                                                                                            
|10.330 |  | Term Sheet effective as of September 3, 2004 with Roche Diagnostics GmbH. (We have omitted certain information from the Term Sheet and filed it separately with the Securities and Exchange Commission pursuant to our request for confidential
treatment under Rule 24b-2. We have identified the omitted confidential information by the following statement: "Confidential Treatment Requested".)
|10.519 |  | Corporate Governance Guidelines, as amended and restated, incorporated by reference to Exhibit 10.519 of Chiron's Form 10-Q for September 30, 2004.(1)                                                                                                                                                                                                                                              
|10.626 |  | Letter Agreement dated July 7, 2004, between Ursula B. Bartels and Chiron, incorporated by reference to Exhibit 10.626 of Chiron's Form 10-Q for September 30, 2004.*(1)                                                                                                                                                                                                                            
|10.627 |  | Supplemental Pension Agreement dated as of July 20, 2004, between Chiron and William G. Green, incorporated by reference to Exhibit 10.627 of Chiron's Form 10-Q for September 30, 2004.*(1)                                                                                                                                                                                                        
|31.1   |  | Certification of the Chief Executive Officer pursuant to Rules 13a-14(a) and 15d-14(a) promulgated under the Securities Exchange Act of 1934, as amended.                                                                                                                                                                                                                                           
|31.2   |  | Certification of the Chief Financial Officer pursuant to Rules 13a-14(a) and 15d-14(a) promulgated under the Securities Exchange Act of 1934, as amended.                                                                                                                                                                                                                                           

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CHIRON CORPORATION    December 16, 2004    SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, Chiron has duly caused this report to be signed on its behalf by the undersigned thereunto
duly authorized.

|                        |  | CHIRON CORPORATION
|----------------------- |  | ------------------
|DATE: December 16, 2004 |  | BY:               
|DATE: December 16, 2004 |  | BY:               

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