The changes of the body temperature, intensity of oxidative processes, glucose content in the blood, and unesterified fatty acids (UEFA) content in the serum of the homeotherm organism were studied at +5 degrees C. The initial (1--3) coolings induced mobilization of carbohydrate and fat energetic reserves, using the blood free glucose and the serum UEFA for heatproduction. This caused hypoglycemia in some of the animals. Further (4--13) coolings were characterized by considerable fluctuations of the parameters. Excessive release of UEFA from the fat stores and their enhanced oxydation coincided with a small drop of the body temperature and a decrease in glucose concentration in the blood. By the 26th-35th exposures the animals became adapted to the temperature +5 degrees C. In the adapted organism, the prevalence of UEFA oxydation coincided with the prevalence of the free glucose entering the blood. This suggests that, in the cold-adapted organism, oxydation of UEFA keeps up the body temperature while using the blood glucose is restricted. This may be of importance for a steady maintenance of glucemic homeostasis in cold.