Effects of zolpidem, a short acting non benzodiazepine hypnotic, have been studied in eight female poor sleepers, aged 25 to 54 years, documented during two consecutive adaptation nights. Subjects were recorded according to a 22 day single blind study. Placebo was given orally at bedtime on nights 2-4, zolpidem on nights 5-20 and finally placebo on nights 21-22. Polygraphic recordings (conventional analysis) were performed on nights 1-6; 12, 13; 19-22. Parameters of sleep continuity, sleep architecture and cyclical structure of sleep were studied. Zolpidem 10 mg showed a hypnotic effect on poor sleepers. It reduced sleep latency, increased total sleep time and decreased the number of awakenings during all recorded nights. During the first post-drug night a rebound insomnia was observed in two subjects only. Zolpidem did not increase specifically stage 2 to the detriment of stages 3 and 4 but it restored them during the first nights of administration. Study of the rapid eye movements-non rapid eye movements (REM-NREM) sleep cycles structure showed that the increase of stages 3 and 4 occurred only during the first part of the night. Finally, zolpidem had no effect on REM sleep temporal distribution.