The average induction dose of thiopentone did not differ significantly when 8 young women were compared with 8 young men. In neither group did the dose increase with increased body weight. Clearance of thiopentone from venous blood was described by a 3 compartment open model. The average volumes of V1 and V3 were greater in the females, but only the difference between the V3 values was significant (P < 0.05). Significant correlations (P < 0.01) were found between the initial drug concentrations and the K12 values. The slopes of the regression lines were 0.0029 for the women and 0.0038 for the men (0.1 < P < 0.2). Apparently, the redistribution rate constant k12 is predominant in determining the sleep dose rather than the initial distribution volume V1.