controlled clinical trial was carried out on forty-nine patients with mania, acute psychoses or exacerbation of a chronic psychosis to compare zuclopenthixol acetate with haloperidol to determine the efficacy and adverse effects during a six day trial period. Both zuclopenthixol acetate and haloperidol were equally effective in patients with acute psychosis, exacerbation of chronic psychosis and in maniZuclopenthixol acetate produced a greater degree of sedation in the initial phase of treatment and caused fewer extrapyramidal side effects than haloperidol and the patients treated with zuclopenthixol acetate needed less anti-parkinsonian treatment.