The plasma 1-deoxyglucose contents of non-diabetic and streptozotocin-induced diabetic rats, were measured by gas-liquid chromatography. The mean values of the compounds in non-diabetics were 1.11±0.23 mg/dl, and in diabetics, 0.25±0.18 mg/dl. The difference was statistically significant by Student's t-test (p≤0.05). It was confirmed that the plasma 1-deoxyglucose contents in diabetic rats before insulin therapy were already low, compared to those of non-diabetics, and were sometimes undetectable. It is suggested that plasma 1-deoxyglucose determination might serve as a useful metabolic parameter for evaluating the function of carbohydrate metabolism in diabetes mellitus.