Adult white rats were exposed daily during 30 days to 2-hour heating (40--41 degrees)--adaptation, and then were transferred to ordinary temperature conditions at 25--27 degrees--desadaptation. The initial period of adaptation revealed a decrease of the liver glycogen content and a relatively constant level of glycemia. A considerable activation of the carbohydrate digestion enzyme systems followed this lowering of energy resources. Metabolic regulatory mechanisms seem to take part in this activation which plays an adaptive role in maintenance of constant glycemia level under these stressful conditions.