The serum concentrations of different glycosaminoglycan fractions have been studied in diabetic subjects without evidence of vascular complications and compared with those of age-and sex-matched normal subjects. Electrophoretic analysis of the various glycosaminoglycan fractions showed an increase in hyalunoric acid and heparin, and a decrease in heparan sulfate, chondroitin-4-sulfate and chondroitin-6-sulfate. Furthermore, the levels of glycosylated haemoglobin A1 were positively correlated with those of hyaluronic acid (r = 0.96, p. less than 0.001) and heparin (r = 0.45, p less than 0.01) in the diabetic group. The present data suggest thah a) in diabetics there is a shift in the metabolism of glycosaminoglycans towards a decreased sulfated glycosaminoglycans/hyaluronic acid ratio; and b) long-lasting hyperglycemia is correlated with the disturbances in the metabolism of glycosaminoglycans.