In an attempt to elucidate the mechanism of action of adenosine, specific adenosine binding was determined by using plasma membrane rich microsomal fraction of dog coronary and carotid arteries. The binding of adenosine to both coronary and carotid preparations was temperature as well as pH dependent and was inhibited by aminophylline and adenosine nucleotides. Scatchard analysis of the saturable binding data on carotid arteries exhibited a single species of binding sites with a Kd value of 1.34 x 10(-6) M and binding capacity of 140 pmol/mg of protein. The first order dissociation rate constant of adenosine binding to carotid preparation was 0.0247 min-1. The nonlinearity of equilibrum binding data (Scatched Plot) and dissociation curve of binding to coronary arteries suggested the presence of more than one population of binding sites. The data suggest that the binding sites located in the microsomal fraction of coronary and carotid arteries possess the basic characteristics of the receptors which might be involved in the vasodilatory action of adenosine.