African-American women have a substantially higher prevalence of hypertension and suffer greater morbidity and mortality due to blood pressure elevation than white-American women. Much of this ethnic difference in blood pressure is due to increased obesity in African-American women. In contrast, young African-American and white-American girls have similar levels of obesity and blood pressure. The hemodynamic changes that occur with developing obesity and result in this ethnic difference in blood pressure have not been well characterized. Cross-sectional studies of adolescents have shown that despite similar blood pressure levels, African-Americans have higher total peripheral resistance while whites have higher cardiac output. Cross-sectional studies of adults show that obesity is associated with elevation of cardiac output. If such an obesity-related increase in cardiac output is superimposed on the underlying elevation of total peripheral resistance in African-American girls, these hemodynamic factors could be responsible for the developing ethnic divergence in blood pressure seen in late adolescence as African-American girls develop an increasing prevalence and severity of obesity.