Electrolyte and fluid transport across the corneal epithelium plays an important role for the maintenance of corneal transparency. Little is known about the cellular mechanisms underlying the transepithelial transport phenomena. We have therfore started to investigate the transmembranal transport processes in cultured corneal epithelial cells. Studies were performed in an established corneal epithelial cell line from the rabbit (SIRC cells) and in primary cultured bovine corneal epithelial cells. In these cells, intracellular pH was continuously measured using the pH-sensitive absorbance of intracellularly trapped dimethylcarboxyfluorescein. In both cell types, SIRC cells and cultured bovine corneal epithelial cells, evidence was found in favor of a sodium-dependent and amiloride-sensitive Na/H exchange. In cultured bovine corneal epithelial cells, Na/H exchange was shown to play an important role in intracellular pH recovery after an acid load. Furthermore, as has been demonstrated in other epithelia, Na+/H+ exchange may also be important for transepithelial corneal transport.