Biochemical changes in blood, i.e. glucose, ketone bodies, lactate, protein, blood urea nitrogen (BUN), and free alanine before and after surgical stress were measured in normal and diabetic rabbits. Both the normal and diabetic rabbits were divided into two groups; the acute phase (0 to 180 minutes after surgery) and the subacute phase (1 to 3 postoperative days). Surgical stress was induced by performing laparotomy under anesthesia. Glucose, ketones, lactate, BUN, and alanine were higher in diabetic than normal animals. Protein level was lower in the diabetics. In the acute phase, normal and diabetic animals showed a similar reaction. In the subacute phase, ketone bodies and BUN increased predominantly in normal animals with no change of glucose levels. In two of the diabetics, an increase in glucose, lactate and alanine was seen. These phenomena support Bessman's postulation of stress which has two of phases, the catecholamine phase and the pituitary-adrenal phase. It is considered that this reaction to surgical stress in the acute phase is due to glycogenolysis i.e., glucose from glycogen and lipolysis i.e., ketones from fat induced by catecholamine, and that increased ketone bodies and glucose levels in the subacute phase are due to ketogenesis i.e., ketones from protein and gluconeogenesis i.e., glucose from protein. In both phases ketonemia is predominant in normal rabbits after surgical stress, suggesting that insulin does not reduce directly lipolysis in the acute phase and ketogenesis in the subacute phase, under conditions of stress.