X0201 3/A 2003-05-16 2003-05-21 0 0000706539 CHIRON CORP CHIR 0001233539 PATTERSON LEONE D 4560 HORTON STREET EMERYVILLE CA 94608 0 1 0 0 Vice President, Controller Common Stock 3099 D Employee Stock Option (Right to Buy) 21.4688 2000-02-26 2009-02-26 Common Stock 4687 D Employee Stock Option (Right to Buy) 31.875 2000-08-31 2009-08-31 Common Stock 917 D Employee Stock Option (Right to Buy) 53.75 2001-08-31 2010-08-31 Common Stock 8200 D Employee Stock Option (Right to Buy) 46.97 2002-08-31 2011-08-31 Common Stock 11000 D Employee Stock Option (Right to Buy) 38.775 2003-08-31 2012-08-31 Common Stock 9000 D This report is being amended to correct the typographical error that appeared under column 2, Table I of Reporting Person's Initial Statement of Beneficial Ownsership of Securities filed on May 21, 2003 with the SEC. Each of the forms filed since May 21, 2003 overreported Reporting Person's end-of-period holdings by 1,455 shares. This amount includes 1,900 share rights which are subject to certain vesting. Employee Stock Option granted under the Chiron 1991 Stock Option Plan in transaction exempt under Rule 16b-3. Right to exercise vests as to 1/4 of the total shares on the first anniversary of the grant date and montly thereafter as to 1/48 of the total shares, subject to acceleration of vesting upon certain qualifying terminations of employment. The Chiron 1991 Stock Option Plan has provisions permitting, in the discretion of the Administrator, the withholding of shares from the grant to satisfy income tax withholding. Leone D. Patterson by Naima Robinson as Atty-in-Fact 2004-03-31