β-Glucuronidase (β-G) and N-acetyl-β-glucosaminidase (NAG) activities were investigated in diabetic patients. Serum β-G activity, NAG activity, total cholesterol (TC), triglyceride (TG) and atherogenic index (A.I.) were significantly higher in diabetics than in controls. In diabetics, there were significantly positive correlations between serum β-G activity and fasting blood glucose level, TC, TG and A.I., and between serum NAG activity and fasting blood glucose level, TC and TG. Serum β-G and NAG activities were significantly higher in diabetics with hyperlipidemia than in diabetics without hyperlipidemia. The elevation of serum β-G and NAG activities in diabetics might be due to metabolic abnormalities accompanying hyperglycemia and hyperlipidemia. Serum NAG activity was significantly higher in diabetics with nephropathy than in those without nephropathy. β-G activity of polymorphonuclear leukocytes (PMN) in poorly controlled diabetics was significantly lower than PMN-β-G activity in controls and fairly controlled diabetics. Degradation of mucopolysaccaride and glycoprotein might be impaired in poorly controlled diabetics, and this impairment might explain glycoprotein-deposition in diabetic microangiopathy and impaired bacteriocidal activity in diabetic leukocytes. PMN-β-G activity was significantly higher in diabetics with severe diabetic retinopathy (ScottⅢ-V) than in those with mild diabetic retinopathy (Scott I-Ⅱ). This data suggests that high PMN-β-G activity contributes to the establishment of diabetic microangiopathy.