[3H]Spiroperidol labeled dog area postrema membranes with high affinity (KD, 0.1 nM) and stereospecificity. The displacement of the radioligand by different dopamine agonists and antagonists indicated that the labeled sites were dopaminergic in nature. Guanine nucleotides decreased agonist affinity for the labeled sites without affecting the affinity for antagonists. Adenylate cyclase in the area postrema was stimulated by guanine nucleotides and sodium fluoride but not by dopamine. The results suggest that the dopamine receptor in the area postrema can be classified as D2-type receptors.