Ethnic differences in drug response have been extensively reported, and ethnicity has been suggested to be useful clinically as a predictor of drug response. Genetic polymorphisms in the genes encoding beta(1) adrenergic receptor (AR) and beta(2) AR, targets of beta AR antagonists, and in cytochrome P4502C9, the enzyme involved in warfarin metabolism, have the potential to explain some of the observed ethnic variability in drug response and to improve clinical practice.