Greater mortality and morbidity for cardiovascular events and renal complications have been reported in black than in white hypertensive patients. In this study we examined whether race per se affected markers of early target organ damage in a population of black and white hypertensive patients in whom casual as well as ambulatory blood pressure measurements were obtained. We assessed renal and systemic hemodynamics by measuring mean arterial pressure invasively, renal blood flow by 131I-para- aminohippuric acid clearance, and cardiac output by the indocyanine dye dilution technique. Left ventricular structure was determined by two- dimensional guided M-mode echocardiography. No significant differences in cardiac output, total peripheral resistance, renal blood flow, and renal vascular resistance were found between the two racial populations. Indices of myocardial structure were also comparable between black and white hypertensive patients. This was true regardless whether all patients were analyzed, or male patients only, or only those with elevated ambulatory blood pressure measurements. When defining arterial pressure by 24-h ambulatory monitoring, no differences in early target organ damage can be found between black and white patients with mild essential hypertension.