We examined the types of guanine nucleotide-binding regulatory (G) protein subunits in isolated glomeruli, cortices excluding glomeruli and medullas of rat kidneys using bacterial toxin-catalyzed adenosine 5’-diphosphate (ADP) ribosylation and specific immunoblots. ADP ribosylation catalyzed by cholera or pertussis toxin revealed the presence of stimulatory G (Gs) or inhibitory G (Gi) proteins in membranes of the 3 segments of the kidney. Immunoblots further demonstrated the existence of several G-protein subunits, two Gs-protein α-subunits (Gαs: 45 and 52 kD), Gi-protein α1, α2 and α3-sub units (Gαi1, Gαi2:40–41 kD, Gαi3: 40 kD), bacterial toxin-insensitive G-protein αq- and α11-subunits (Gαq/11: 42 kD) and G-protein β-subunits (Gβ: 35-36 kD), in membranes of the preparations. The predominant subspecies of Gαs was a 52-kD protein in glomerular membranes and a 45-kD protein in membranes of cortices and medullas. All of the G-protein subunits examined, however, were not detected in cytosolic fractions of glomeruli, cortices and medulas. Thus, we conclude that detectable quantities of several G-protein subunits including the new G-protein subunit, Gαq/11, are present in membranes of glomeruli, cortices not containing glomeruli and medullas from the rat kidney. Both the existence of Gαil and/or Gαi2 subunits in glomeruli and the presence of Gαq/11 subunits in the 3 preparations are new evidence. Moreover, the current study indicates the existence of the predominant subspecies of Gαs subunits in the 3 distinct segm