Abstract The actions of catecholamines and adrenergic blocking drugs on the veins of the dog (posterior vena cava, portal vein, femoral vein, lateral saphenous vein) were studied in vitro . In these experiments quantitative and qualitative differences were found. Superficial veins were more sensitive. Adrenaline and dopamine had direct actions causing contractions blocked by phenoxybenzamine (pM50-6.40) and erotamine (pA2-8.20). Isoprenaline caused relaxation and/or contraction depending on the vein, tone and dose; relaxation was blocked by pronethalol (pA2-6.51) and contractions were antagonized or reversed by ergotamine and phenoxybenzamine. Evidence for the existence of both alpha and beta receptors in the veins, the former prevailing, is presented. Ergotamine induced marked venoconstriction, at least in part through alpha receptor activation; no evidence for a beta blocking action of ergotamine was found. The results in vivo (autoperfused femoral vein, vena cava, and small veins of the paw) correlate well with those found in vitro . Agonists and antagonists exerted effects which can be attributed to the presence of alpha and beta adrenergic receptors. However, in these experiments isoprenaline never caused activation of alpha receptors, probably because the doses used were much lower than those used in vitro .