The sleep pattern of a hypomanic patient, was studied for 17 of 25 consecutive nights during which time he received no drug therapy. There was a marked reduction in actual sleep time and in slow-wave sleep and a modest reduction in stage 1 rapid eye movement (REM) sleep. There was increase in time awake and drowsy, and there was an abnormal mixture of wave forms. There is a striking similarity between the sleep pattern of this patient and that recorded from psychotic depressives. This may be of importance in furthering our understanding of the relationship between mania and depression.