A study has been made of the temperature dependence of the active sodium transport system of the isolated abdominal skin of Rana pipiens. The method of measuring the current across the short-circuited skin has been used to determine the net sodium flux. In addition, potential measurements were made on the unshunted skin. Typical experiments illustrative of the observed temperature effects are presented. A skin, bathed on both sides by sodium Ringer's solution, was subjected to repeated gradual changes in temperature from 0–30°C while the current was monitored. The current was found to have a temperature coefficient of 6.9%/°C in the range 5–15°C, corresponding to a Q 10 of 2.0, but above 25°C the coefficient was negative and the transport system appeared relatively unstable. In other experiments the sodium concentration of the solution bathing the external skin surface was varied (substituting choline) from 0–100% sodium Ringer's solution, while the temperature was maintained constant at 20°, 10° and 2.5°C. The net sodium flux with 10-% sodium Ringer's solution showed temperature coefficient of 9–10%/°C. Analyzing the data in terms of a model carrier system, the stoichiometric dissociation constant of the carrier-sodium complex, the passive conductance, the active transport conductance, and the transport potential were computed. The dissociation constant shows no consistent temperature dependence. The two conductances show positive temperature coefficients of 4–5%/°C and 1–4%/°C respectively. The transport potential was found to increase with temperature by 7%/°C. The energy dissipation of the transport system is discussed with reference to reported oxygen consumption measurements of the frog skin. Our data suggest that the transport process becomes increasingly efficient as the temperature is lowered.