This study demonstrates the existence of adenosine receptor(s) in a homogeneous population of cultured smooth muscle cells and intact muscle strips from rabbit aorta. Binding assays with <sup>3</sup>H-adenosine were performed using the crude microsomal fraction of the cultured cells. Adenosine binding was reversible and displayed a single species of saturable binding sites. The nuclear and soluble fractions showed negligible binding. Adenosine uptake blockers (e.g., nitrobenzylthioinosine, dipyridamole) had no effect on its binding. Theophylline inhibited the binding and the relaxation of aortic strips to adenosine. The data suggest the existence of specific binding sites for adenosine on the surface of aortic smooth muscle cells.