Sheets of utricular epithelium from gerbil were mounted in a micro-Ussing chamber. Step changes in [Na] and [K] on each side of the epithelium led to changes in transepithelial potential difference (Vt) and resistance (Rt) which were consistent with the presence of ionic conductances for these two ions. Responses of Vt to 20 mM Rb steps were similar to those to 20 mM K steps. Several common Na and K channel blockers were applied: No evidence for the presence of amiloride-sensitive Na channels was found. At 10(-6) M, amiloride caused no significant changes in Vt but at 10(-3) M it initially decreased or increased Vt when applied from the apical or the basolateral side, respectively. Ba and quinidine each reduced Vt, quinidine more strongly from the basolateral than from the apical side. Tetraethylammonium, another K channel blocker, had no significant effect from either side. These data suggest that in spite of the low value of Rt, the cellular pathway contributes significantly to the voltage response to cation concentration steps in this epithelium. The mode of action of 10(-3) M amiloride and the K channel blockers remains uncertain.