Proximal tubules were isolated from the rat kidney by collagenase digestion of the cortical tissue followed by Percoll gradient centrifugation. Microscopic and hormone-stimulated adenylate cyclase activity studies proved the purity of the preparation. [3H]Prazosin, [3H]rauwolscine, and [125I]iodocyanopindolol were used to identify and quantitate respectively the alpha 1-, alpha 2- and beta-adrenergic receptors. Proximal tubular (F4) particulate fraction was compared against other cortical nephron segment (F1, F2) fractions and the total collagenase-digested cortex particulate suspension (Ft). Proximal tubules were enriched in alpha 1- and alpha 2-adrenergic receptors compared with Ft (alpha 1-receptor, 100.4 +/- 4.5 vs. 87.4 +/- 4.9; alpha 2-receptor, 250 +/- 16.2 vs. 185.1 +/- 12 fmol/mg protein). The fractions enriched in glomeruli and distal tubular segments (F1, F2) had relatively low concentrations of alpha 1- and alpha 2-adrenergic receptors. In contrast, beta-adrenergic receptor concentration in the proximal tubules was approximately 25% of that in the Ft fraction and approximately 10% of that in the F1 fraction. Isoproterenol-stimulated adenylate cyclase activities in the different fractions corroborated well with the pattern suggested by the [125I]iodocyanopindolol binding studies. Our results suggest that whole-cortex preparation radioligand binding studies may reflect proximal tubular alpha 1- and alpha 2-adrenergic receptor changes quite well. They may, however, miss or give erroneous impressions about beta-adrenergic receptor changes occurring in different cortical nephron segments.