The clinical effects of chlorpromazine (CPZ) administered in accordance with a double-blind design in one of three doses (200, 400 or 600 mg) were examined in 44 psychotic patients. The relationships between the effects and the CPZ concentrations in plasma and cerebrospinal fluid (CSF) were analyzed. The antipsychotic and side effects were rated according to the CPRS and the Simpson and Angus scale. CPZ concentrations were measured by a mass fragmentographic method. Treatment with CPZ resulted in a significant reduction of morbidity scores, without any clear dose relation. The final outcome was more favourable in women than in men. Extrapyramidal side effects but not somnolence were positively dose related. The antipsychotic effects tended to be positively related to the dose of CPZ in mg/kg as well as the CPZ concentrations in plasma and CSF. The greatest number of significant correlations between the CPZ concentration in CSF and the morbidity scores were seen after 2 weeks of treatment. The results indicated marked clinical improvement with CPZ concentrations above 1 ng/ml in CSF and 40 ng/ml in plasma. After 4 weeks of treatment the correlations between the CPZ concentrations and the clinical improvement were still positive but the coefficients were lower than at 2 weeks and only occasionaly significant. Extrapyramidal symptoms were significantly related to the CPZ concentrations in plasma and CSF. Somnolence was significantly related to the CPZ concentrations in CSF.