The effect of pimozide, a potent and specific blocker of central dopaminergic transmission, upon the sleep of man was studied in six healthy volunteers. Given at doses of 1 and 4 mg, which have clear central effects in humand. pimozide produced only minor changes in the EEG patterns of sleep. At these doses a slight and non-significant decrease in phase I sleep was observed, while phases W,II,III,IV and REM were not modified. No differences were noted between drug or post-treatment and control nights in total NREM sleep, total REM sleep, number of episodes of REM or total number of eye movements. An increase in REM sleep in the first REM period in the first drug night were the only statistically significant findings. If one accepts that central effects seen in man after pimozide given in conditions similar to those of this study are due to dopaminergic blockade, our results tend to suggest that dopamine is, at most, of rather minor importance in the physiology of sleep in man.