Fifty schizophrenic in-patients (DSM-IV) were treated in an open study with zuclopenthixol acetate. Mental status, improvement and side-effects were measured before administration of the drug as well as after the 1st, 2nd and 3rd injection. Positive and negative symptoms were evaluated with the use of PANSS. 60% of patients received three injections. Usually the intervals between injections lasted 48 hours. The improvement after the 3rd injection of zuclopenthixol acetate was found in 80% of patients. All positive symptoms improved after the treatment (p < 0.001), among them excitement (54% reduction vs. baseline), hostility (49%) suspiciousness/persecution (45%). The study revealed that parallel to the decrease of positive symptoms, the severity of negative symptoms also decreased, in particular: difficulty in abstract thinking (28%) and stereotyped thinking (27%) (p < 0.001). Passive/apathetic social withdrawal and lack of spontaneity as well as flow of conversation only slightly improved (p < 0.05). 50% of patients experienced side-effects--usually extrapyramidal reactions.