The effects of 6-hydroxydopamine (6-OHDA) on the isolated portal vein and caudal artery of the rat were studied to investigate the possibility of producing in vitro adrenergic denervation of these blood vessels. Loss of nerve function was determined by field stimulation of the nerves, using short pulses, and by 3H-norepinephrine (NE) uptake. Addition of 6-OHDA produced contractions of both veins and arteries. Two hours after treatment with 6-OHDA, the contractile responses of the caudal arteries and portal veins to field stimulation were reduced to undetectable levels. At this point, the vessels were unable to take up 3H-NE and incubation of the preparations with l-NE failed to restore the contractile responses to nerve stimulation. Prejunctional supersensitivity to l-NE was observed in the portal vein after 6-OHDA but hot in helically cut strips of caudal artery. Prejunctional supersensitivity of the caudal artery to NE was seen, however, if the vessel geometry was kept intact, suggesting that the uptake mechanism for catecholamines only plays a major role in the termination of action of exgenous NE when norepinephrine is applied through the nerve plexus. We conclude that in vitro treatment with 6-OHDA rapidly produces functional adrenergic denervation of both portal vein and caudal artery of the rat and provides an accurate assessment of the importance of the neuronal uptake mechanism to NE sensitivity.