The effects of 25 mg propiomazine were examined in ten healthy volunteers in a sleep laboratory setting. A significant decrease in sleep latency and a corresponding decrement in subjectively assessed sleep latency was found during drug treatment. The distribution of the different sleep stages was affected to a relatively small extent. Some evidence for a suppression of REM-sleep in the early part of the treatment period was found. Based on subjective assessment, the subjects rated their sleep quality as significantly improved during treatment. Ratings of "drowsiness in the morning" were not different during baseline and drug treatment, but there was a significant decrease at withdrawal.