Abstract: Objective: To study the changes of the level of urinary acetylglucosaminidase(N-acetyl-β-D-glucosaminidase,NAG) in patients with chronic renal failure(CRF) and its clinical significance in the development of CRF.Methods: Eight-seven patients were divided into 2 groups according to the stability of the disease and the level of blood pressure;and thirty healthy persons acted as controls.Their NAG activity was measured by colorimetry test and compared.Results: The urinary NAG level in CRF patients was significantly higher than that of the controls(P<0.01).The urinary NAG level in patients with unstable CRF was significantly higher than that in patients with stable CRF(P<0.01),and the urinary NAG level of CRF patients with hypertension was higher than that of patients without hypertension(P<0.01).Conclusions: The instability of CRF and hypertension may be pivotal factors that aggravate tubulointerstital injury.