Over 3 months, 13 Caucasian and 16 Asian schizophrenic patients were sequentially treated with weight-adjusted fixed doses and clinically determined, variable doses of haloperidol. During the fixed-dose phase, Asians had a slightly higher mean serum haloperidol concentration and a significantly higher rating for extrapyramidal symptoms. During the variable-dose phase, the Asian patients' mean required dose was significantly lower, resulting in lower serum haloperidol concentrations at the first emergence of extrapyramidal symptoms and for optimal clinical response. These results indicate pharmacodynamic differences in therapeutic response but no significant difference in steady-state serum concentration between the two groups.