Experiments were performed to investigate why cooling augments the contractile responses of superficial veins, but depresses that of deep limb veins. Rings of dog's saphenous veins were mounted in an organ chamber for isometric tension recording. Cooling (from 37 to 24 degrees C) depressed the tissular uptake of [3H]norepinephrine and potentiated the contraction caused by norepinephrine and sympathetic nerve stimulation; this potentiation persisted after inhibition of the disposition mechanisms for the catecholamine and in the presence of ouabain or iproveratril. The affinity of the alpha adrenoceptors, to judge from the KA values for norepinephrine and from the pA2 values for the competitive antagonist phentolamine, was significantly greater at 24 degrees C than at 37 degrees C. Thus, an instantaneous change in the affinity of alpha adrenoceptors explains the augmented response of the cutaneous veins to adrenergic stimulation. By contrast, cooling depressed the response of femoral veins to norepinephrine and did not significantly affect the affinity of alpha adrenoceptors in this preparation, indicating that the temperature sensitivity of alpha adrenoceptors in cutaneous veins is related to chronic exposure to variations in local temperature.