The relationship between the daily oral dose of the benzamide amisulpride and the striatal D2-dopamine receptors occupancy was investigated in 11 schizophrenic patients using positron emission tomography with 76Br-bromolisuride. The patients were studied before and during chronic treatment with amisulpride over a wide range of doses. The test-retest variability of the method was estimated to be 5.8% in a group of four patients receiving placebo. A curvilinear relationship was demonstrated between the amisulpride doses and the D2-receptor occupancy. A range of 70-80% occupancy of the striatal D2 receptors, suggested as an optimal interval for therapeutic action on positive psychotic symptoms, was obtained with doses of amisulpride ranging between 630 and 910 mg per day, while an occupancy of 85%, suggested to be associated with pronounced extrapyramidal side-effects, was reached with 1,100 mg per day.