210 HbA1 percentage tests were determined in 52 ambulatory insulinodependent patients. There was a close correlation between HbA1 and blood-glucose of the previous two months: mean post-prandial, mean daily and, less strongly, mean fasting blood-glucose. The level of glycosylated haemoglobins correlated significantly with blood-glucose of the same time and highly with mean 24 hour glycosuria 0/00 of previous two months. There was also a slight inverse correlation between HbA1 and uricemia. No correlation resulted with total lipemia, serum triglyceride levels, serum total cholesterol levels and HDL cholesterol concentrations. The increased proportions of HbA1 did not not appear to be related to the age of the patients or to the duration of diabetes or to complications. HbA1 measurement is a simple and objective test of metabolic control in diabetic subjects.