Adenosine (10(-9)-10(-6) mol/l) and R-phenylisopropyladenosine (10(-9)-10(-7) mol/l) partially inhibited the intracellular accumulation of cyclic AMP induced by isoproterenol, prostaglandin E1, histamine and 5'-N-ethylcarboxamidoadenosine in lymphocytes. In contrast, S-phenylisopropyladenosine, which is a poor agonist of the adenosine A1/Ri receptor, had essentially no inhibitory effect. 8-Phenyltheophylline, in low concentrations that do not inhibit cyclic AMP phosphodiesterase, completely blocked the inhibitory effect of R-phenylisopropyladenosine on the increase in cyclic AMP induced by prostaglandin E1. R-Phenylisopropyladenosine (10(-8)-10(-6) mol/l) also inhibited the cyclic AMP accumulation in lymphocytes induced by forskolin (10(-5) mol/l), which activates adenylate cyclase through direct interaction with the enzyme. We also investigated the presence of the adenosine A1/Ri receptor on human polymorphonuclear leukocytes. R-Phenylisopropyladenosine (3 x 10(-9)-10(-7) mol/l) abolished the stimulating effects of prostaglandin and forskolin on cyclic AMP accumulation in polymorphonuclear leukocytes. This effect was blocked by 8-phenyltheophylline and was not observed with the stereoisomer S-phenylisopropyladenosine. The results support the existence of an A1/Ri receptor that regulates cyclic AMP metabolism of human lymphocytes and polymorphonuclear leukocytes.