In order to investigate physiological reactions to various surrounding temperature, 45 heads of rabbits (2.4-3.6 ㎏) were caged under different temperature and relative humidity (Optimal; 20℃/60%),(Heat stress: 37℃/80%, and Cold stress; 0℃/45%). Blood was collected from the rabbits treated with heat and cold for two and four hours. Clinical symptoms, blood pictures, values of total serum protein and its fractionation and that of blood glucose were analyzed. The results are summarized as follows. Body weight and heart rate of rabbits were not affected by cold (down to 0℃) and heat (up to 37℃) stress in four hours, but body temperature and respiration rate were significantly (p$lt;0.01) affected by heat stress. 2. Much variation in red blood cell count was not found after cold and heat treatments, but slight decreases in level of hemoglobin and packed cell volume were found after the treatments. 3. Heat and cold stress caused a slight decrease of white blood cell count. In its differential count, pseudoeosinophils were significantly (p$lt;0.01) increased. On the other hand lymphocytes were significantly (p$lt;0.01) decreased. Eosinophils were started to increase in four hours under cold stress condition (p$lt;0.05). Meanwhile basophils and monocytes were not changed. 4. Total serum protein values were not changed throughout this experiment. In its fractionation, except of increase in γ-globulin no other fractionated protein has been changed. 5. Blood glucose value was significantly (p$lt;0.01) increased under cold stress condition. From these results it can be concluded that hematological physiology of animals is affected by heat and cold stress.