A method was evolved for studying potassium and sodium transport without labelled ions in the frog skin. The potassium secretion sharply increased after the nystatin had been added to the solution near the skin surface. Suppression of the apical membrane sodium permeability with amiloride or triamterene did not alter the potassium secretion velocity. The nystatinum increased the potassium and sodium permeability. The blocking agents for sodium channels became ineffective in the presence of nystatin. During the nystatin action on the apical membrane, the work of the Na/K pump does not change in the basal plasmatic membrane, while suppression of the pump with strophantin abolishes the potassium secretion. Therefore, the potassium secretion level depends on the apical membrane potassium permeability and is independent of the sodium transport across this membrane; it is due to potassium inflow into the cell with the aid of Na/K pump of the basal plasmatic membrane.