After 6 weeks of fixed dose oral haloperidol treatment. Chinese schizophrenic patients (in the People's Republic of China) had 52% higher plasma haloperidol concentrations than U.S. non-Asian schizophrenic patients. Chinese and U.S. patients were matched for sex and body weight. The difference in plasma drug concentrations may explain why Asians are reported to require smaller dosages of neuroleptic drugs than non-Asians, and why they may be more sensitive to neuroleptic-induced side effects. When prescribing haloperidol to persons of Asian ancestry, physicians should consider that higher than expected plasma haloperidol concentrations and an increased sensitivity to haloperidol may occur.