Cutaneous and pulmonary CO2 loss were measured simultaneously in bullfrogs, Rana catesbeiana, at either 10, 20 or 30 degrees C. Arterial blood samples were taken in each experiment and analysed for [H+] and total plasma [CO2]. These values were used to calculate Pa(CO2) by means of the Henderson-Hasselbalch equation. Both [H+] and Pa(CO2) increased with temperature as previously observed. Skin CO2 loss was measured using a titration method. (At 30 degrees C it was necessary to add calcium hypochlorite (5-9 ppm) to block bacterial growth and respiration). Skin CO2 loss rose with temperature but the mean fraction of the total CO2 lost by this route decreased from about 50% at 10 degrees C to less than a third at 30 degrees C. At each temperature, over 90% of an incremental increase in total CO2 loss was excreted via the lungs while skin loss was relatively constant over a wide range of total loss values. The increase in skin CO2 loss with temperature corresponded to a proportional increase in the estimated transcutaneous P(CO2) difference. (This difference was assumed to equal Pa(CO2) minus ambient P(CO2.) Consequently, the skin CO2 conductance (skin CO2 loss/transcutaneous P(CO2) was not significantly influenced by temperature. This apparent temperature independence of skin CO2 conductance may be important for acid-base regulation of skin breathers in response to temperature change.