Eleven patients suffering from chronic insomnia were given 30 mg flurazepam for 28 nights. While EEG measures of total sleep time and sleep efficiency were improved, changes in sleep latency and intermittent waking time were small and nonsignificant. Subjective benefits in sleep were confined to the first 2 nights. There was neither increased nor decreased daytime sleepiness. Cognitive functioning was significantly decreased during the first 2 days, and patients were unaware of these changes. Simple motor tasks were relatively unaffected. Desalkylflurazepam concentrations showed significant accumulation over time, but were not predictive of sleep measures or daytime performance in individual subjects. The withdrawal period was characterized by subjectively disturbed sleep and daytime dysphoria.