As the prototypic "atypical neuroleptic," clozapine plays an increasingly important role in the treatment of refractory psychotic patients. However, little is known about the efficacy and safety of the compound for Asian patients. This study compares dosage, efficacy, and side-effect profiles in 17 Korean-American and 17 Caucasian age- and sex-matched schizophrenia or schizoaffective patients treated with clozapine. Asians showed a greater change than Caucasians in total scores of the 8-item Brief Psychiatric Rating Scale while receiving a significantly lower mean dose of clozapine (t = 2.48; p < .025). Furthermore, Asians had significantly lower mean clozapine concentrations than Caucasians and were significantly more likely to experience anticholinergic and other side effects. No serious untoward effects, such as agranulocytosis were reported in either group. These data suggest that Asians may be treated effectively and safely with lower doses of clozapine than those used for Caucasians.