Ethnicity is one factor that may account for the observed differences in both pharmacokinetics (PK) and pharmacodynamics (PD) of drugs, resulting in variability in response to drug therapy. Given that the applicability of clinical study results to the treatment of an individual patient is a critical consideration in a physician's choice of drug therapy, drug development should seek to ensure that a clinical pharmacologic evaluation includes a population that is representative of the target therapeutic population. Ethnic diversity in drug response with respect to safety and efficacy and the resulting differences in recommended doses have been well described for some drugs. Some of these differential responses may be related to the pharmacogenomics of a particular drug. Pharmacogenomic techniques have recently enjoyed widespread use in studies of drug exposure and response. The clinical relevance of variability in drug response due to pharmacogenomics of drug-metabolizing enzymes was considered at a September 2004 workshop cosponsored by the US Food and Drug Administration (FDA), Johns Hopkins University, and the Pharmaceutical Research and Manufacturers of America (http://www.fda.gov/cder/Offices/OCPB/workshops.htm).