The purpose of this study was to evaluate the effects of acute heroin withdrawal on waking behavior and slow wave sleep. Data were collected from drug-dependent patients who were using pure heroin and from drug-free controls. All data were recorded on a 24-hour per day basis for 5 - 7 consecutive days. EEG records were manually scored according to standard criteria. The heroin-dependent patients during withdrawal showed approximately a 26% decrease in slow wave sleep and an 18% increase in waking behavior. The awake state in the heroin-dependent patients during withdrawal also displayed an increase in number of episodes and number of state shifts, and a decrease in duration and sleep onset latency. In addition, the slow wave sleep categories during withdrawal generally showed an increase in sleep onset latency and interstate interval and a decrease in number of episodes. These results indicate that heroin withdrawal is associated with a marked disruption of the central nervous system mechanisms responsible for maintenance of the normal sleep--waking cycle. Analyses of the pattern of this disruption will further aid in understanding the withdrawal syndrome.