Microinjections of selective agonists for adenosine receptor subtypes were made into the caudal NTS of rats. CGS 21680, a selective A2 receptor agonist, elicited pronounced, dose-related decreases in mean arterial blood pressure (ED50 = .021 nmols/rat). Conversely, CPA, a selective A1 receptor agonist, elicited potent dose-related increases in mean arterial blood pressure (ED50 = 0.185 nmols/rat). Additionally, the depressor responses elicited by the A2 agonist and the pressor responses elicited by the A1 agonist were completely and selectively blocked, respectively, by the selective A2 antagonist, CGS 15943A, and the selective A1 antagonist, DPCPX. These data indicate that selective activation of brainstem adenosine receptors in vivo may elicit distinct and opposing response patterns.