This 4-week, double-blind, randomized study was undertaken to determine the dose-response relationship of amisulpride in 319 patients with acute exacerbation of schizophrenia. Fixed doses of amisulpride (400, 800 and 1200 mg/day) and haloperidol (16 mg/day) were compared to amisulpride, 100 mg/day, as a potentially subtherapeutic dose. Efficacy data (BPRS total score and PANSS positive subscale) in the amisulpride groups generated a bell-shaped dose-response curve, with 400 mg/day and 800 mg/day being the most effective treatments for positive symptoms. Parkinsonism did not increase significantly between baseline and endpoint with amisulpride 400, 800 and 1200 mg/day compared to the amisulpride 100 mg/day group, whereas the difference was significant for haloperidol (P<0.05). It is concluded that amisulpride 400 mg and 800 mg/day is highly effective in treating the positive symptoms of schizophrenia, with less extrapyramidal side-effects than haloperidol 16 mg/day.