Pharmacotoxic psychoses resulting from therapy of advanced Parkinson's disease can occur in up to 60% of the patients. Treatment must not be completely discontinued in such cases. Clopenthixol (Sordinol, Ciatyl) in small dosage has been shown to be much more effective than all other types of therapy in the management of those psychoses. In a group of 28 patients treated with clopenthixol the progression of Parkinson's disease was not quicker than a control group of 30 patients not treated with clopenthixol. Both groups were of similar age and at a similar stage of the disease.