Biochemical pathways which are involved in energy metabolism were examined in the kidney of heat acclimated hamsters. It was found that heat acclimation caused 47% reduction in glucose 6 phosphatase (Glc 6 Pase) activity and 40% lower rate of gluconeogenesis. No changes were found in the activity of hexokinase, glucose 6 phosphate dehydrogenase, pyruvate kinase, lactic dehydrogenase, or in kidney glycogen content. Isolated kidney mitochondria of heat acclimated hamsters utilized 15% less oxygen than that of controls, but no differences were found in the P/O ratio. Determination of the content of some cytochromes showed a significant reduction in cytochromes c + c1, but no difference was found in the content of cytochromes a, a3, and b. These results suggest that the kidney plays a role in the reduction of energy metabolism during the process of heat acclimation.