The following statements can be made on the basis of our study. 1. The butyrophenone bromperidol is an absolutely effective drug of the series of very high-potency neuroleptics, with a mean neuroleptic threshold dose of 5.6 mg/day. The mean optimum dose is 6 mg/day, and the mean maximum dose reaches 11 mg/day, i.e. twice the neuroleptic threshold dose. 2. The substance is generally well tolerated; when it was administered to one third of all cases in one single dose in the evening, it not only had the same beneficial neuroleptic-antipsychotic effect as on administration t.i.d., but also positively influenced sleep, so that sleep-inducing drugs could be reduced and, in some cases, even dispensed with. This relatively long-lasting effect confirms the finding made in animal experiments.