Summary Renal vasoconstriction induced by intra-arterial administration of 1 μg of norepinephrine or renal nerve stimulation was enhanced during adenosine infusion in concentrations from approximately 2.5 × 10-9 to 10-7 g/ml while the vasoconstrictor response to adenosine itself was inhibited. Enhancement of the vasoconstrictor response to norepinephrine and inhibition of that to adenosine were dependent on the infusion rate of adenosine. After interruption of adenosine infusion, the initial responses to norepinephrine and adenosine recovered promptly. Thus it appears that adenosine modulates the adrenergic effect in the renal circulation.