1. The efficacy of butoctamide hydrogen succinate (BAHS) was compared with that of nitrazepam on the basis of the polysomnograms and the subjective assessments. 2. Twelve healthy male students were divided into three groups consisting of 4 subjects each with were administered BAHS 600 mg, nitrazepam 5 mg, and BAHS 600 mg + nitrazepam 5 mg, respectively. 3. Polygraphic recordings were made for 8 consecutive nights for each subject, and the polysomnograms were evaluated by computerized automatic analysis using the interval histogram method. 4. An inert placebo was administered on the first 3 nights and on the seventh and eighth nights, and the test article regimen was administered on the fourth, fifth and sixth nights. 5. The test articles and the placebo were administered orally at 22:30 hr, and the recording of polysomnograms was started at 23:00 hr and ended at 8:00 hr the next morning. 6. The subjects were requested to fill out the subjective assessment of sleep before falling asleep and after arising the next morning. 7. BAHS increased REM sleep and decreased stage 2 sleep significantly; however, it failed to affect stage 1, 3 or 4 sleep. 8. Nitrazepam increased significantly the total sleep time and stage 2 sleep but decreased significantly the stage 3 sleep and decreased slightly the stages 1, 4 and REM sleep. 9. The combined treatment with BAHS and nitrazepam did not alter the sleep parameters except for increasing the total sleep time. 10. No obvious changes were observed in the subjective assessments after administration of the drugs. 11. These findings suggest that BAHS results in a unique sleep pattern different from benzodiazepines, and that BAHS may be suitable for treating insomnia in elderly patients and those with drug abuse, manic-depressive illness or schizophrenia.