The responsiveness of alpha- and beta-adrenergic receptors was assessed in 13 black and 13 white borderline hypertensive and normotensive men, matched for age and body mass. White borderline hypertensives showed significantly decreased responsiveness of cardiac beta-adrenergic receptors and vascular beta 2-adrenergic receptors to intravenous isoproterenol. In contrast, black borderline hypertensives showed no evidence of decreased beta-adrenergic receptor responsiveness. Vascular alpha 1-adrenergic receptor responsiveness, assessed by pressor response to phenylephrine, was unrelated to blood pressure, but was significantly greater in black than in white men. These preliminary observations suggest that there may be racial differences in adrenergic receptor mechanisms involved in the pathogenesis of hypertension.