The concentration of 1-deoxyglucose(1,5-anhydroglucitol) in plasma from patients with insulin-dependent diabetes mellitus was measured by gas-liquid chromatography with an all-glass capillary column. Twenty-one plasma samples were obtained from 21 patients before insulin therapy, and 34 more from 13 patients receiving insulin therapy. 1-Deoxyglucose was generally not detectable in plasmas of diabetic patients before they received insulin; it was measurable in the patients who had received insulin, although its concentration was low compared with that of healthy subjects. We therefore suggest that the absence of 1-deoxyglucose in plasma is one of the markers of metabolic states of diabetes, perhaps reflecting a disturbed function of carbohydrate metabolism; its presence in plasma within a normal range may reflect the better control of diabetic patients.