X0201 4/A2003-08-312003-09-12 0000706539 CHIRON CORP CHIR 0001233539 PATTERSON LEONE D 4560 HORTON STREET EMERYVILLE CA 94608 0100ControllerCommon Stock2003-08-314F018050.54D4541DThis total includes 1,400 share rights awarded pursuant to the Chiron 1991 Stock Option Plan in transaction exempt under Rule 16b-3, which share rights are subject to certain vesting.The amount of securities beneficially owned includes Reporting Person's purchase of 167 shares under Issuer's Employee Stock Purchase Plan, which purchase was not reportable under Section 16(a) of the Securities Exchange Act of 1934, as amended.Leone D. Patterson by Carolyn Mar-Andreotti as Atty-in-Fact2003-09-12