To clarify the effects of hypoxia on stimulus-evoked noradrenaline release and on neuronal reuptake of the released noradrenaline, we examined the effects of hypoxia on contraction responses of rabbit thoracic aortic strips to transmural electrical stimulation and on the stimulation-evoked overflow of total [3H] and [3H]noradrenaline from the strips prelabelled with [3H]noradrenaline. This was done in the presence or absence of an inhibitor of neuronal uptake (cocaine). In a medium equilibrated with a gas mixture of 95% O2/5% CO2 (control), cocaine doubled the stimulation-evoked overflow of total [3H] and [3H]noradrenaline; there was a concomitant increase (130%) in contractions to electrical stimulation. At 0% O2 (95% N2/5% CO2, hypoxia), cocaine had no significant effects on either the stimulation-evoked overflow of total [3H] and [3H]noradrenaline or contractions. In the absence of the drug, hypoxia decreased the stimulation-evoked overflow of total [3H] and [3H]noradrenaline to 47% and 43%, respectively, of the control values, whereas these values were 31% and 28%, respectively, after exposure to cocaine. The inhibition by hypoxia of contraction responses to electrical stimulation was greater in the presence of cocaine than in its absence. These results show that hypoxia inhibits both noradrenaline release evoked by a given stimulus and neuronal uptake.