In order to define the adrenergic receptors in small pial blood vessels, we studied [3H]dihydroalprenolol (DHA) binding, [3H]dihydroergocryptine (DHE) binding, and catecholamine-stimulated adenylate cyclase in membranes prepared from the hog pia. [3H]dha bound to a saturable number of sites (0.09 pmol/mg protein) with a high affinity to (10 mM). The ability of a small series of adrenergic agents to compete for [3H]DHA binding was as expected for binding to beta-adrenergic membrane receptors. The receptor binding appeared to be composed largely of beta 2-adrenergic sites but some sites with beta 1 properties were detected. The beta-adrenergic agonist, isoproterenol, stimulated adenylate cyclase activity by 20% in pial membranes in the presence of GTP. The potency of catecholamines in stimulating adenylate cyclase correlated well with theif sites (0.39 pmol/mg) on these membranes. alpha-Adrenergic agents were potent competitors for [3H]DHE binding but dopamine, serotonin and histamine had effects only at high concentrations. These data demonstrate the presence of alpha- and beta-adrenergic membrane receptors and beta-adrenergically stimulated adenylate cyclase activity in small pial blood vessels from the hog.