THE increasing variety of and demand for sedative and hypnotic drugs have created a dilemma for the physician. Until recently, little sound scientific data was available to him which could be utilized in selecting appropriate drugs for the treatment of insomnia. Studies of the effects of drugs on sleep relied essentially on nurses' observations and subjective reports. With current all-night electrophysiological records, however, it is now possible to determine accurately when an individual is asleep, what type of sleep he is in and how sleep is affected by various drugs. Over the past several years, our laboratory has systematically evaluated a number of commonly used hypnotic agents. Preliminary reports of these investigations, primarily relating to rapid eye movement (REM) sleep alterations, have appeared elsewhere.1-3 This paper presents a comparative analysis of studies relating the administration and withdrawal of three hypnotics in varying dosages to effects upon all sleep stages