Adult amphibian skin actively transports Na from its apical to basolateral side while in turn, K is recycled through Na , K -ATPase and K channels located in the basolateral membrane. We previously found that PRL stimulates Na transport in the skin of the adult tree frog (Hyla arborea japonica) via an increase in the open-channel density of the epithelial Na channel (ENaC). If PRL also activates basolateral K channels, this activation would help to stimulate Na transport, too. Whether PRL does indeed stimulate basolateral K channels in the adult tree frog was examined by measuring the short-circuit current across nystatin-treated skin. Both tolbutamide, a K_ATP channel blocker, and tetrapentylammonium (TPA), a K_Ca channel blocker, blocked the current, the effect of TPA being more powerful than that of tolbutamide. Contrary to expectation, PRL inhibited the basolateral K channels in this skin. In the presence of basolateral amiloride, PRL still inhibited the basolateral K current, suggesting that the Na -H exchanger located in the basolateral membrane does not mediate the inhibitory effect of PRL on the basolateral K channels in Hyla.