N-Acetyl-β-D-glucosaminidase (abbreviated to as NAGase) is an enzyme in lysosome which is contained abundantly in the renal tubular epithelia and is related to the degradation of mucopolysaccharides and glycoproteins.

It is recognized that the NAGase in urine increases in various cases of renal diseases or after an operation of the kidney and the NAGase in urine as well as serum increases in case of diabetes. In the field of clinical and animal experiments, the measurement of the NAGase has attracted an interest in connection with diagnosis of various renal diseases and also as an indicator in examining nephrotoxicity. In the prior art, p-nitrophenyl N-acetyl-β-D-glucosaminide and 4-methylumbelliferyl-N-acetyl-β- D-glucosaminide have generally been used in the determination of the NAGase activity.