Contributions of the receptor and basolateral membranes to the resting potential in bullfrog taste cells were studied by replacing the superficial and interstitial fluids of the tongue by various salines. When the interstitial K+ concentration ([K+]0) was increased to 100 mM, the resting potential decreased by 45%. A similar increase in superficial [K+]0 decreased the resting potential by 15%. A simultaneous increase in both superficial and interstitial [K+]0 to 100 mM decreased the resting potential by 60%. Total removal of Na+ from either the superficial or interstitial fluid increased the resting potential by 40%. Ouabain (10(-4) M) in the interstitial fluid decreased the resting potential by 30%, while the drug in the superficial fluid had no effect. Amiloride (10(-3) M) in the superficial fluid hyperpolarized the cells to 145%, while the drug in the interstitial fluid caused no change in the resting potential. Ca2+-free superficial saline reduced the resting potential to 75%. Interstitial Ca2+ did not affect the resting potential. Total removal of either superficial Cl- or interstitial Cl- did not change the resting potential. These results suggest: 1) Na+ and K+ move across the receptor and basolateral membranes of the taste cell down their electrochemical gradients, 2) Na+ is extruded from the taste cell by the Na-K pump which exists only in the basolateral membrane, 3) the resting potential of a frog taste cell consists of the diffusion potentials of Na+ and K+ across the receptor and basolateral membranes, and the potential resulting from the activity of the electrogenic Na-K pump in the basolateral membrane.