Little is known about the relative stoichiometry of guanine nucleotide‐binding (G) proteins relative to the effector systems to which they link. We addressed this question for the stimulatory G protein (G_s) linked to adenylate cyclase. Forskolin stimulates the catalytic subunit of adenylate cyclase (C), but it has a higher efficacy and potency when C also interacts with the G protein G_g. Accordingly, we measured high‐affinity [³H]forskolin binding to intact cells to assay α,‐C complexes. No high‐affinity specific binding occurred with unstimulated cells. The β‐adrenergic agonist isoproterenol promoted the binding of [³H]forskolin to about 3000 sites per cell, suggesting that each receptor on average activates at least several G_g molecules. Activating G_g directly with cholera toxin maximally promoted [³H]forskolin binding to a similar number of sites, suggesting that this is the maximal number of α_g‐C complexes formed per cell. We conclude that each cell likely contains only a few thousand functional copies of C, and that the availability of C (rather than G_g, which exists in more than 100,000 copies per cell) is likely to be limiting for agonist stimulation of adenylate cyclase activity.—Alousi, A.; Jasper, J. R.; Insel, P. A.; Motulsky, H. J. Stoichiometry of receptor‐G_g‐adenylate cyclase interactions. FASEB J. 5: 2300–2303; 1991.