Frogs kept in dilute solutions of Cl- maintain a steady state with respect to this ion. Chloride is exchanged at a rate of about 15 mumol 100 g-1 h-1 (47 nmol cm-2 h-1). Over 90% of the efflux is integumentary of which about 50% is diffusion of the total influx. The rest is carrier mediated, half of which is exchange diffusion and half active transport. The chloride transport system displays saturation kinetics and is inhibited by acetazolamide. Uptake of Cl- is not dependent on concomitant uptake of cations. Salt-depleted frogs accumulate Cl- from dilute KCl or choline chloride in exchange for an endogenous base, probably HCO-3. High bath concentrations of NaCl (greater than 5 mM) abolish the active uptake of Cl- and increase the passive permeability of the skin to Cl-.