SUMMARYFour groups of twenty adult female patients received respectively 0.8, 1.1, 1.4 and 1.7 mg/kg of 1 per cent methohexitone by intravenous injection. The times were recorded when each patient was fully awake and when she was judged clinically fit to go home. It was found that each increase in dosage resulted in a significant prolongation of sleeping time and a linear increase in dosage resulted in a significant prolongation of sleeping time and a linear increase in full recovery time. The results were compared with those obtained previously in a comparable group of female patients who had of 1 mg/kg of propanidid. Within the dose ranges studied an increase of 1 mg/kg of methohexitone produced the same increase in duration of sleep as did 6.5 mg/kg of propanidid.