A longterm investigation containing three distinct studies has been carried out in order to clarify efficacy and inocuity of clopimozide in the maintenance treatment of chronic psychotics. Twelve patients took part in the pilot study (Study I) during which the optimal weekly dose was established to be 24 mg. These patients were then subdivided into two groups for a controlled study with placebo (Study II). This double-blind evaluation has clearly established the superiority of cloprimozide over placebo. Patients were evaluated at the start and completion of the study with three scales. During the surveillance period (Study III), clopimozide was administered daily with a mean dose of 2.5 mg. Results were equally satisfying as those obtained during weekly treatment. The appearance of side-effects, mostly akatsia and dyskinesia, was only noted during the weekly administration. They could be efficiently controlled with dexetimide.