Abstract The effect of pertussis toxin pretreatment on the putative A 3 receptor-mediated hypotensive response to N 6-2-(4-aminophenyl) ethyladenosine (APNEA) has been investigated in the anaesthetised rat. Pertussis toxin pretreatment essentially abolished the bradycardia induced by the prototype A 1 receptor agonist, N 6-cyclopentyladenosine, whereas the fall in blood pressure induced by the selective A 2A receptor agonist, CGS 21680 was enhanced. Pertussis toxin substantially reduced the hypotensive response to APNEA. In this respect, the mechanism of action resembles that of the cloned A 3 receptor which when expressed in CHO cells couples negatively to adenylate cyclase by a pertussis toxin-sensitive mechanism. The data provide further evidence that adenosine A 3 receptors mediate the hypotensive response to APNEA in the rat.