Blacks have increased hemodynamic responses to both physiological and pharmacological adrenergic stimulation compared with whites, and this may contribute to the greater prevalence of hypertension in this ethnic group. A small study suggested enhanced α1-adrenoreceptor-mediated arterial vasoconstriction in the forearm vasculature of blacks compared with whites, but it is unknown whether this reflects a generalized vascular phenomenon. The objective of this study was to examine the hypothesis that there are ethnic differences in venous α1-adrenoreceptor responsiveness. Using a linear variable differential transformer, we measured local dorsal hand vein responses to increasing doses of the selective α1-adrenoreceptor agonist, phenylephrine, in 106 subjects (64 whites and 42 blacks). There was wide interindividual variability in responses to phenylephrine. The dose that produced 50% of maximal constriction (ED50) ranged from 11 to 5442 ng/min, and maximal venoconstriction (Emax) ranged from 13.5% to 100%. Blacks (geometric mean ED50 =172 ng/min; 95% confidence interval, 115-256 ng/min) were more sensitive to phenylephrine than whites (310 ng/min; 95% confidence interval, 222-434 ng/min; unadjusted P=0.026; adjusted P=0.003). Median Emax was slightly higher in blacks (89%; interquartile range, 82% to 98%) compared with whites (85%; interquartile range, 75% to 95%; P=0.07). Taken together with previous findings in arterial vessels, our results suggest a generalized increased sensitivity to α1-adrenoreceptor-mediated vasoconstriction in blacks. Increased vascular α-adrenoreceptor sensitivity could predispose to hypertension, and future studies addressing the contribution of this mechanism to ethnic differences in the prevalence of hypertension will be of interest.