Plasma methohexitone concentrations were determined in 30 children, aged one to six years, who received 25 mg.kg-1 rectal methohexitone as either a two per cent or ten per cent solution for induction of anaesthesia. Venous blood samples were obtained 15, 30, 45 and 120 minutes following drug administration. Twenty-six of 30 children were asleep within fifteen minutes. Mean plasma methohexitone concentrations were 5.39, 4.42, 3.40 and 1.54 micrograms.ml-1 at 15, 30, 45 and 120 minutes following administration of two per cent methohexitone. Use of the ten per cent solution resulted in mean plasma methohexitone concentrations of 3.81, 3.12, 2.31 and 1.07 micrograms.ml-1 at the same time intervals. Plasma methohexitone concentrations were significantly higher at 15, 30 and 45 minutes following administration of two per cent methohexitone, when compared to the ten per cent solution.