Chiron 10-Q 2003 Q2 Quarterly report

QuickLinks -- Click here to rapidly navigate through this document

Exhibit 32.1

CHIRON CORPORATION

SECTION 1350 CERTIFICATION

        In connection with the periodic report ofCHIRON CORPORATION, a Delaware corporation (the "Company"), on Form 10-Q for the period ended June 30, 2003, as filed with the Securities and Exchange Commission (the "Report"), I,HOWARD H. PIEN, Chief Executive Officer of the Company, hereby certify as of the date hereof, solely for purposes of Title 18, Chapter 63, Section 1350 of the United States Code, that to the best of my knowledge:

(1)

the Report fully complies with the requirements of Section 13(a) or 15(d), as applicable, of the Securities Exchange Act of 1934, and



(2)

the information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company at the dates and for the periods indicated.

        This Certification has not been, and shall not be deemed, "filed" with the Securities and Exchange Commission.

Date: August 12, 2003 By: /s/  HOWARD H. PIEN      HOWARD H. PIEN
President and Chief Executive Officer

QuickLinks

Exhibit 32.1

CHIRON CORPORATION SECTION 1350 CERTIFICATION