Freshly isolated frog skin initially gains or loses water in proportion to the square root of the time elapsed after its immersion. In solutions of NaCl to which it is fully exposed, the gain or loss is linearly related to the concentration of the salt in the solution. If exposed only on its outer surface, the skin taken from pithed frogs likewise gains or loses in linear relation to the concentration of NaCl in the medium, at rates at least 1/2 of those found in the pithed intact frog. This fact refers the initial exchanges of water by the intact frog to the skin itself. Chlorides are exchanged by isolated skin at rapid rates which are in linear relation to the concentration of NaCl in the medium. The rate of the circulation bore no measurable relation to the concentration of the fluid being transported by it. In a few experiments in which the circulation was stopped altogether, the rates of osmosis into or out of intact frogs were the same as for normal intact frogs.