The authors present the results of a clinical investigation of triflupro-mazine (Siquil) in psychotic patients. The patients were classified in the following nosological groups: schizophrenia, 15 cases; mania, 5 cases; involutional psychosis, 2 cases; arteriosclerotic agitation, 1 case. The authors emphasize the sedative potency of the drug. The therapeutic dose for psychotic patients varied between 150 and 300 mg daily. This dose can, therefore, be considered 4 to 5 times lower than the therapeutic dose of chlorpromazine. The fundamental difference between "therapeutic dose" and "sedative dose" is stressed. The latter, which should be given to ambulatory patients (neurotic or psychotic patients on maintenance doses) should vary between 25 and 100 mg. daily. The authors remark that insufficient doses are often the cause of failure in the treatment with the drug. The period of treatment was from 25 to 90 days. All the patients were on maintenance doses. Side effects were minimal and severe reactions were not observed. There were 14 cases of impregnation syndrome (56 per cent of the patients). The authors are of the opinion that this syndrome should not be considered a side effect but rather a desirable occurrence in the treatment of psychotic patients. Results obtained were considered very good and 17 patients (73 per cent) were discharged. Of the 6 patients in whom no results were obtained, 3 were chronic cases. The authors conclude that Siquil, apart from being a potent sedative, is also effective in the treatment of psychotic patients.