We sought to characterize regional heterogeneity of astrocytes using adrenergic receptor sites as cellular markers. Primary cultures made from 6 regions of neonatal rat brain consisted almost exclusively of astrocytes. Membranes from astrocytes cultured 1-3 weeks were prepared for radioligand binding assays of beta- and alpha 2-adrenergic sites using the ligands [3H]dihydroalprenolol and [3H]p-aminoclonidine, respectively. Receptor expression was not affected by time in culture. Astrocytes from different brain regions varied up to 3-fold with respect to number but not affinity for both classes of adrenergic binding site with a rank order of cerebral cortex = superior colliculus greater than hippocampus = ventral midbrain greater than or equal to caudate nucleus greater than or equal to hypothalamus. Binding to beta- and alpha 2-adrenergic receptors was positively correlated across brain regions. Astrocytic receptor binding in each region did not correspond to total receptor levels assessed by quantitative autoradiography. We conclude that: (a) astrocytes are markedly heterogeneous between major brain regions with respect to expression of adrenergic binding sites; (b) regional variations in the density of adrenergic binding sites in brain reflect, in part, local specialization of astrocytes; and (c) a substantial proportion of the adrenergic binding sites in some brain regions may be on astrocytes.