Adrenaline and noradrenaline were infused in cumulative doses into the brachial artery of six healthy volunteers and changes in forearm blood flow (FBF) were measured by plethysmography. The catecholamines were infused together with saline, yohimbine and doxazosin, in that order. All infusions were given in the presence of intra-arterial propranolol to prevent beta-adrenoceptor-mediated effects. Adrenaline and noradrenaline reduced FBF significantly. This decrease in FBF was significantly attenuated by doxazosin as well as by yohimbine. No differences were found between adrenaline and noradrenaline. It is concluded that postjunctional alpha 1- and alpha 2-adrenoceptors are involved in the vasoconstriction caused by exogenous adrenaline and noradrenaline in man. The relevance of circulating adrenaline for the alpha 2-adrenoceptor-mediated contribution to basal vascular tone remains to be established.