Guanine nucleotide binding proteins (G-proteins) are heterotrimeric proteins involved in signal transduction in epithelia. In addition to possessing a polarized epithelium the nephron is composed of well defined segments, each with distinct receptors, transporters and other functions. Since different G-proleins interact with different receptors, a differential distribution of the various G-protein subunits would be expected. To investigate this possibility, polyclonal antipeptide antibodies to several G-protein subunits were used to examine the distribution of these proteins in nephron segments and their localization to apical or basal membrane domains. Immunoblotting of cortical membrane vesicles demonstrated the presence of G-proteins in both the brush border and basolateral membrane. Staining with Gα common and Gαs antibodies demonstrated more of these G-protein subunits in the brush border than basolateral membrane. G-protein β subunits were also present in greater quantity in brush border membranes, Immunoeytochemical analysis demonstrated good antigenic preservation and basically confirmed the results of immunoblotting of renal cortex. G-proteins were also found to be differentially distributed in the medulla, the amounts increasing with proximity to inner medulla. Only Gαs, and Gβ subunits were demonstrated in glomeruli. but all subunits examined were detected in brush borders of proximal and apical membrane of distal tubules in cortex. In outer medulla Gαs. was detected in both basolateral and brush borders of some tubules and only brush borders of others, Gαi2 and Gβ were found in brush border and Gαi3 was not detected in this area. Basolateral membranes of inner medulla contained Gαs, Gαi3, and Gβ subunits; Gαi3, was also present in apical membranes in some tubules. Gαi2 was detected only in apical membranes in this region. We conclude that G-proteins are differentially distributed in nephron segments. Investigation of regional tubular function may disclose a role for the G-proteins we have localized.