Two methods were used to investigate cellular ion transport processes in confluent monolayers of cultured bovine corneal epithelial cells: measurements of membrane voltage (V) using conventional microelectrodes, and intracellular pH (pHi) measurements using the pH sensitive absorbance of intracellularly trapped 5(and 6)-carboxy-4′,5′dimethyl-fluorescein.(1) V averaged-39.2±0.9 mV (mean±SEM, n=71) with a range of-30 to-59 mV. Increasing extracellular potassium depolarized the cell membrane with a K+-slope of 43.3 mV/decade [K+] (for [K+] between 20 and 80 mM). Intracellular as well as extracellular acidification reversibly depolarized the cell membrane. Depolarization induced by 40 mM K+-pulses was smaller at extracellular pH (pHo) of 6.9 as compared to pHo= 7.9. These findings are compatible with a pH-sensitive K+conductance.(2) During steady state pHiwas 6.96±0.05 (mean±SEM, n=7). After intracellular acidification, induced by Nh4Cl-prepulse technique, pHiwas regulated back towards normal steady state pHi. Application of 1 mM amiloride reversibly inhibited pHirecovery. Furthermore, pHibackregulation was inhibited by removing sodium from the extracellular solution. The effect was reversible after readdition of sodium. These findings suggest that a Na+/H+exchange is present in corneal epithelial cells and participates in pHibackregulation after an intracellular acid load.