Vanadate stimulates adenylate cyclase activity in turkey erythrocyte membranes. The maximal stimulation is 7-fold over basal at 3 mM vanadate; higher concentrations are inhibitory. A suboptimal concentration of fluoride (1 mM) together with vanadate (3 mM) activates adenylate cyclase in a non-additive manner; cyclase activation by optimal fluoride (10 mM) is inhibited by vanadate (3 mM). There is no stimulation by vanadate of adenylate cyclase activity (measured either with Mg2+ or Mn2+) in CYC- S49 lymphoma cell membranes. Vanadate (3 mM) shows no effect on binding of Beta-adrenergic agonists or antagonists to the [3H] (-)-dihydroalprenolol binding site in turkey erythrocyte membranes. These results suggest that the effect of vanadate on Adenylate cyclase is mediated through the nucleotide regulatory protein and may act by a mechanism similar to fluoride. However, in cholera toxic-treated membranes as well as in GDP-beta-S plus isoproterenol-treated membranes, fluoride-stimulated adenylate cyclase activity is significantly reduced, but vanadate stimulation is not. Our results suggest that although the actions of vanadate and fluoride in adenylate cyclase may each involve the nucleotide regulatory unit, the exact mechanisms of activation by the two anions differ.