Ethnic differences in vascular adrenergic responsiveness have been implicated to be a potentially important mechanism which may be responsible for some of the variations in haemodynamic patterns between races. These differences may account for the variability in the prevalence of hypertension in different groups. The main aim of this study was to determine whether there was a difference in venous responsiveness to the vasoactive agents, phenylephrine and isoproterenol, between Mexican-Americans and White Americans.Isoproterenol is a potent non-selective ␤-adrenergic agonist, phenylephrine is an ␣ 1 -selective adrenergic agonist. Using the dorsal hand vein compliance technique, dose-response curves were constructed for the