Thiopentone was given to eight women and eight men (60–79 yr). The disappearance of thiopentone from the venous blood was described by a three-compartment open model. The only significant difference between the sexes was a higher initial venous concentration in males. The dose (mg kg ⁻¹) for induction was 70% of the value (P<0.05) previously reported for a comparable group of younger men and women (20–40 yr). The volumes of distribution V₂ and V₃ were larger in the elderly (P<0.05). The terminal half-lives were increased with advancing age (from 75% to 100% on average) (P≤0.01). The clearance value was 50% greater in the older women than in a group of young women. For all groups a significant correlation between initial drug concentration and k₁₂ supported the hypothesis that the redistribution rate constant k₁₂ is the predominant factor in the pharmacokinetic profile of a dose of thiopentone sufficient to obtund the eyelash reflex.