SummaryThis review focuses on the fact that, for aldosterone to play its role as a regulator of blood volume through its sodium-retaining action, chloride must be retained as well. In fact, amphibian skin reacts to this hormone in terms of chloride conductance as well as active transepithelial sodium transport, both of which increase. The ions move along distinct transepithelial pathways, the principal cells being involved in sodium transport, and mitochondria-rich cells in chloride movement. In this context, it is relevant to emphasize that the collecting duct of mammalian nephron is also heterogeneous in terms of cell types.