We have investigated the subtype of alpha-adrenoceptor responsible for the contractile effect of dopamine using isolated human saphenous vein. Lengths of saphenous vein were obtained surplus to coronary artery bypass graft operations and studied as intact rings using a conventional organ bath technique. Contractile responses to dopamine (10(-7)-10(-3) M) in the presence of propranolol, cocaine, and 17 beta oestradiol were competitively antagonised by the alpha 2-selective adrenoceptor antagonist yohimbine (10(-8)-10(-6) M) but unaffected by the alpha 1 selective adrenoceptor antagonist doxazosin (10(-8)-10(-6) M), whereas the response to norepinephrine (NE) (10(-8)-10(-3) M) was antagonised by doxazosin (10(-8)-10(-6) M), thus demonstrating the presence of alpha 1-adrenoceptors in this preparation. We conclude that the contractile effects of dopamine in isolated human saphenous vein are mediated predominantly by an action on alpha 2-adrenoceptors.