The stoichianetry of the Na-Cl ootransport mechanism at the base-lateral membrane of the frog corneal epithelium was studied with the aid of intracellular microelectrodes by analyzing the effects of ouabain on intracellular recordings (PDSC) and transepithelial short-circuit current (ISC). Under short-circuit conditions, the total current across the basolateral membrane was equated to the Cl−transport across the apical membrane. Ouabain produces a quick and steep decrease of PDSC(7.1 mV) and ISC(3.0μA/cm2) that was ascribed to a sudden inhibition of the electrogenic component of the Na-K pump. From these effects, and from results in previous studies, the maximum value for the Na+flux via the ootransport mechanism (ICNa) was estimated and compared to the apical Cl−transport (a minimum estimate of the Cl−flux cotransported with Na+). In all experiments, Iclwas larger than INa. Considering that Na+also recirculates across tne basolateral membrane via a passive pathway, the Cl:Na flux ratio of the ootransport system may be as high as 4.