We report the study of 6 hospitalized depressed patients studied for a total of 153 nights in the sleep laboratory. While there is considerable intersubject and intrasubject variability, the findings from this and earlier studies indicate that the sleep disturbance in hospitalized depressed patients is pervasive and affects most parameters of sleep. Sleep is fragmented and light with an increase in awake and drowsy time and a major and protracted decrease in delta wave sleep. There are marked fluctuations in stage 1 rapid eye movement sleep and suggestions of a long standing deficiency in this stage of sleep. The detailed findings are considered in relationship to the particular clinical syndrome and also in relation to findings from patients with other clinical diagnoses. The issue of whether specific changes are uniquely associated with particular syndromes is considered. Emphasis is placed on the need for careful longitudinal studies with carefully described groups of patients so that the interactional effects of a variety of variables can be more carefully considered.