In rabbit aortic smooth muscle, adenosine inhibited the increase induced by norepinephrine (NE) in 45Ca uptake in the presence of KCl (under low affinity Ca2+ uptake conditions) and the NE-induced decrease in 45Ca uptake (under high affinity Ca2+ uptake conditions). Basal 45Ca uptake and KCl-stimulated 45Ca uptake were not altered by adenosine. 2. Adenosine blocked the NE-induced contraction (in high K+) and inhibited both the tonic and phasic components of the NE-induced contraction. 3. Thus, adenosine selectively inhibits release of the intracellular Ca2+ store important for the phasic response to NE and that Ca2+ uptake component important for the NE-induced tonic response.