SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

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                                    FORM 8-K

                                 CURRENT REPORT

                       Pursuant to Section 13 or 15(d) of

                       the Securities Exchange Act of 1934

        Date of Report (Date of earliest event reported): April 21, 2004


                               Chiron Corporation
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             (Exact name of registrant as specified in its charter)


     Delaware                   0-12798                    94-2754624
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  (State or other             (Commission                (IRS Employer
  jurisdiction of             File Number)             Identification No.)
  incorporation)

                 4560 Horton Street, Emeryville, CA              94608
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               (Address of principal executive offices)        (Zip Code)


Registrant's telephone number, including area code (510) 655-8730
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                                       N/A
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          (Former name or former address, if changed since last report)




Item 12. Results of Operations and Financial Condition.

On April 21, 2004, Chiron Corporation (the "Company") announced via press
release the Company's preliminary results for the first quarter ended March 31,
2004. A copy of the Company's press release is attached hereto as Exhibit 99.1
and is incorporated by reference herein.

The information in this Current Report on Form 8-K, including the exhibit
attached hereto, is furnished pursuant to Item 12 and shall not be deemed to be
"filed" for the purposes of Section 18 of the Securities Exchange Act of 1934,
as amended, or otherwise subject to the liabilities of that section.

                                   SIGNATURES

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

                                          CHIRON CORPORATION

Date:    April 21, 2004               By:   /s/ WILLIAM G. GREEN
                                          ----------------------------
                                          William G. Green
                                          Senior Vice President,
                                          General Counsel and
                                          Secretary


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