Pimozide, a specific dopamine blocking agent, was compared with chlorpromazine in a 4-week double-blind study of the treatment of 40 schizophrenic patients newly admitted to hospital through the emergency room. Dosage was adjusted according to therapeutic effect and during the final week ranged from 10--70 mg/day (median 30 mg/day) for pimozide and 600--1,500 mg/day (median 900 mg/day) for chlorpromazine. Pimozide was found to exert somewhat less of an overall therapeutic effect than chlorpromazine, particularly in highly agitated patients. Women responded better to either treatment than men. A weighted mean of the doses given to male and female patients during the final week suggests that in the treatment of acutely ill patients the mg dose equivalency of pimozide in terms of chlorpromazine is approximately 1:25, considerably lower than estimates from maintenance studies. Pimozide induced significantly more parkinsonian symptoms but less autonomic side effects than chlorpromazine. It is suggested that the weaker presynaptic dopamine blocking effect of pimozide might be responsible for its reduced potency in the treatment of acute schizophrenic symptoms.