Histochemical studies of adrenal cortex of male rats under various hypothermic conditions: ice-water immersion with or without administration of Thiopental Sodium or Phenothiazine-derivatives, rewarming, surgical stress and Cortisone & ACTH administration were performed according to Dempsey's method. 1) Differences in individual were minimum and the respiration, circulation and the course of body temperature reduction were much stable under pharmacological hibernation. 2) Ketosteroids in fasciculata and reticularis zones of adrenal cortex were markedly depleted by cold application, but using anesthetics, especially on pharmadological hibernation, depletion of KS was less. 3) Hypothermia and pharmacological hibernation lessened the changes in adrenal cortex by operativ measures (partial resection of liver) under cooling. 4) Some circulatory and parenchimatous changes by cooling and rewarming were observed histologically in the adrenal cortex. Hemorrhagic changes were seen in the adrenal cortex after cooling to 20,5℃ of body temperature, but were less marked after administration of Phenothiazine-derivatives. 5) Cortisone or ACTH had some protective effects against reduction of weight and histlogical changes of adrenal cortex by cooling.