In the present study we investigated the effects of a single injection of reserpine on dopamine receptor function in rat striatum. The measurement of adenylate cyclase activity indicated that cAMP formation induced by the selective D-1 agonist SKF 82526 was greatly increased 2 and 20 h after reserpine; in contrast, the selective D-2 agonist bromocriptine inhibited by the same extent and with the same potency AC in controls and reserpinized striata. In addition, the density of both D-1 and D-2 receptors, as measured in binding studies with the selective D-1 antagonist [(3)H]SCH 23390 and with [(3)H]spiroperidol respectively, was not affected by the treatment. These results suggest that acute reserpine administration induces a selective up-regulation of the transduction mechanisms associated with D-1 receptors, without changing the functional activity of D-2 receptors.