Nocturnal sleep was studied in eight young normal volunteers (3 female and 5 male students) with polygraphic technique during 2 periods of 10 night each. After 2 adaptation and 2 baseline nights with placebo, they were given methylperone (Buronil) 10 or 50 mg per night during three nights and then again placebo for three withdrawal nights. The study was made double blind. The scoring of the records was done according to the manual by Rechtschaffen and Kales (1968). No changes of sleep stages were seen during the drug periods. The lower dose gave an increase of sleep latency but a decrease of number of awakenings during the night. An increase of REM-periods was shown after 50 mg and also a decrease of REM-latency and REM-density. The only significant change during withdrawal periods was a decrease of REM-sleep after methylperone 50 mg, so there was no "barbiturate type" of withdrawal. The change was also different from that of chloropromazine, which has no clear rebound effect.