In the isolated frog cornea, the effects of 0.1mm epinephrine were measured on both the transepithelial and intracellular electrical parameters. Epinephrine increased the short-circuit current (Isc) and transepithelial electrical conductance (gt) by 176 and 96%, respectively. The effective electromotive driving force for active transepithelial Cl transport (ECl) was 45 mV and agrees with the value forECl calculated by a different technique in the isolated rabbit corneal epithelium (Klyce, S.D., Wong, R.K.S., 1977,J. Physiol. (London)266: 777). With respect to the tear-side bathing solution, epinephrine caused the intracellular potential difference of shortcircuited frog corneas to decrease from −54 to −50 mV (P>0.05). The fractional resistance of the apical membrane {F(Ro)=(Ro/Ro+Ri)} whereRo andRi represent the resistances of the apical and basolateral membranes, respectively, decreased from 0.38±0.06 to 0.23±0.03. Using these values ofF(Ro) and the cellular conductances, the calculated Cl resistances ofRo andRi decreased 4.3- and 2.3-fold, respectively. However, the value forECl calculated from the intracellular electrical measurements (48 mV) did not appear to change since this value was in close agreement with the value forECl calculated from the effects of epinephrine on the transepithelial electrical parameters. Thus, the effects of epinephrine onIsc andgt can be accounted for by increases in the Cl conductance of both the apical and basolateral membranes. Epinephrine caused the potential difference across the basolateral membrane to hyperpolarize by 9 mV. All of these results are consistent with the notion that the steps in transepithelial Cl transport include uphill movement into the cell across the basolateral membrane followed by downhill movement across the apical membrane into the tear-side bathing solution.