An international, multicenter, double-blind study was conducted in 183 patients with a first psychotic episode (provisional schizophreniform disorder or schizophrenia; DSM-III-R) treated with flexible doses of risperidone or haloperidol for 6 weeks. At endpoint, 63 percent of risperidone-treated patients and 56 percent of haloperidol-treated patients were clinically improved (> or = 50% reduction in Positive and Negative Syndrome Scale total scores). Risperidone was better tolerated than haloperidol: the severity of extrapyramidal symptoms was significantly lower in the risperidone-treated patients; significantly fewer risperidone-treated patients required antiparkinsonian medication; and significantly fewer discontinued treatment because of adverse events. A post hoc analysis revealed that low doses of these antipsychotics were efficacious in some patients. Furthermore, the severity of extrapyramidal symptoms and the use of antiparkinsonian medications were significantly lower in patients receiving low doses (maximum, < or = 6 mg/day) than high doses (maximum, > 6 mg/day) of risperidone or haloperidol. These findings are consistent with the suggestion that patients with a first psychotic episode may require low doses of antipsychotic medications. Studies designed specifically to compare low and high doses of antipsychotics are warranted to help optimize treatment for these patients.