Race or ethnic identity, despite its imprecise categorization, is a useful means of identifying population differences in mechanisms of disease and treatment effects. Therefore, race and other arbitrary demographic and physiological variables have appropriately served as a helpful guide to clinical management and to clinical trial participation. The African-American Heart Failure Trial was carried out in African-Americans with heart failure because prior data had demonstrated a uniquely favorable effect in this subpopulation of the drug combination in BiDil. The remarkable effect of the drug in reducing mortality in this study has illuminated an important new mechanism of therapy for heart failure. Application of these findings need not be confined to the population studied, but the observation highlights the need for more precise ways to identify individual responsiveness to therapy.