In the tortoise Testudo hermanni Gmelin exposure to high temperature (40°C) produces the following metabolic modifications: (1) in liver, the concentrations of succinate, malate, citrate, cisaconitate and fumarate are enhanced by the treatment, while in heart muscle the same result was found only for malate and succinate; (2) in skeletal muscle the T.C.A.-cycle compounds are scarcely influenced by high temperatures; (3) the metabolic variations induced by hyperthermia are very similar to those caused in the same species by anoxic conditions. The meaning of such modifications is discussed in the text.