Blood gases and pH and plasma [Na+], [K+], [Cl-] and [lactate] were measured on arterial blood of the large predominantly skin-breathing salamander, the hellbender (Cryptobranchus alleganiensis), at 5, 15 and 25 degrees C, both with and without access to air. Access to air had no effect of any of the acid-base variables, but temperature had significant effects on both pH and PCO2. Blood pH decreased with temperature by about 0.016 unit/degrees C both in vivo and in vitro (over the range studied) which is similar to the change previously observed on other ectotherms. Blood PCO2 rose significantly with temperature while plasma [HCO-3] rose slightly but insignificantly. Other ions were unaffected by temperature. This is the first demonstration that the characteristics ectothermic acid-base response to temperature occurs in a vertebrate respiring exclusively through its skin. We suggest that the response in this animal is essentially passive and uncontrolled and is due to: (1) the proportional effects of temperature upon metabolic CO2 production and blood PCO2, and (2) the temperature-independent CO2 conductance of the skin.