Na/K-ATPase sites in both the secretory and reabsorptive epithelia of isolated and microperfused human eccrine sweat glands are localized cytologically. Localization was accomplished through autoradiography of bound 3H-ouabain, a specific inhibitor of the enzyme. Ouabain binding characteristics were determined to ensure maximum specific binding. Enzyme sites are localized only on the basolateral surface of both epithelia in spite of the fact that sodium transport is reversed, i.e., secretory: blood to lumen and reabsorptive: lumen to blood. In view of these findings and in comparison with other recent observations, the role of Na/K-ATPase in secretory electrolyte transport is questioned.