The hypnotic activity of diazepam was compared with that of inactive placebo in a double- blind, randomized study in 40 surgical patients the night before their scheduled procedures. Diazepam per os (10mg) produces a pattern of response that differed markedly from that of the placebo. The patient receiving diazepam fell asleep sooner, slept more soundly and steadily and more felt they had been helped to sleep, while fewer awoke during the night. The significant difference Was obtained in both hypnotic and ataractic effects between diazepam and inactive placebo. Neither diaxepam nor inactive placbo caused marked changes in vital signs or any serious side effects.