The Australian, dominant this season after wins in Sydney and Malaysia, covered the 3.64-mile course in 2min 08.572sec.
Doohan's Honda team-mate, Shinichi Itoh, was second fastest, 0.977sec behind, and the Japanese Honda rider Takuma Aoki third in 2:09.626. Darryl Beattie, who has twice finished as runner-up to his countryman this season, was fifth in 2:09.667.
In the 250cc category, the former world champion, Tetsuya Harada, set the best practice time of 2:10.075 on a Yamaha, 0.185 ahead of title holder Massimiliano Biaggi. The world 125cc champion, Kazuto Sakata, led the class.
Details, Sporting Digest, page 47