The effects of succinate on the intracellular potential difference, PD, were measured in isolated rabbit ciliary processes. Concentrationdependent increases in the hyperpolarization of PD occurred between 1 and 15 mM succinate in NaC1 Ringers. With 5 mM succinate, there was a 6 mV hyperpolarization. Even though the hyperpolarization of PDIwas comparable with 10 and 15 mM succinate, it was more sustained at the latter two concentrations. Succinate also elicited comparable hyperpolarizations of PDIin either Cl--free or HCO3--free Ringers. Similarly, following incubation with either 0.1 mM DIDS or 3 mM BaCl2the effect of succinate on PDIwas unchanged. Five mM succinate had no effect if it was added after 5 mM malonate. Malonate (5 mM) rapidly reversed a 5 mM succinate-induced hyperpolarization of PDIwhich also suggests a metabolically mediated effect on PDI. An isosmotic substitution of Na+with NMDG Ringers depolarized PDI, whereas PDIdepolarized biphasically during exposure to 0.1 mM ouabain. The addition of 5 mM succinate had no effect on either the time course or the magnitude of the depolarization of PDIduring blocking of the Na+:K+pump with either Na+-free Ringers or ouabain. Taken together, these results show that succinate selectively stimulates the Na+:K+pump, but has no effect on any Cl-, HCO3-or a Ba2+-sensitive K+conductance.