The concentration of glycosylated serum protein (GSP) in 125 normal subjects and 105 diabetic patients was measured. The result showed that the mean value of GSP in diabetic patients increased as compared with that of normal subjects, and the mean , concentration of GSP correlated significantly with that of fasting blood glucose in diabetic patients as well as that the mean value of fasting blood glucose which was determined 1-3 weeks before. The level of GSP may be a sensitive indicator for recent control of diabetes