To evaluate delayed (long-term) effects of acute sarin poisoning on postural balance, nine male and nine female victims of the Tokyo Subway Sarin Poisoning in Japan (sarin cases) were examined by computerized posturography 6-8 months after the poisoning. Their plasma cholinesterase activities (ChE) on the day of the poisoning (March 20, 1995) were 13-95 (mean 68.2) IU/l for females and 19-131 (mean 75.9) IU/l for males, which were not significantly different between the two sexes. In females, the postural sway of low frequency (0-1 Hz) in the anterior-posterior direction and area of sway with eyes open was significantly larger in the cases than in the controls. Romberg quotients for the low-frequency sway in the anterior-posterior direction for females and low-frequency sway and length of sway in the medio-lateral direction for males were significantly related to log ChE. It is suggested that a delayed effect on the vestibulo-cerebellar system was induced by acute sarin poisoning; females might be more sensitive than males.