d glucosaminide and a buffer with which renal dysfunction can be diagnosed precisely quickly and easily application_number US 72365291 A description the present inventors have tried to resolve the problem and achieved the present invention providing a new substrate high solubility and ease of handling the kits of the present invention require no urine blank and can determine the activity by the continuous method furthermore the determination of nagase activity can be performed precisely and quickly even in a case of a very small amount of nagase since the present method has a very high sensitivity sodio 3 3 39 dichlorophenolsulfonphthaleinyl n acetyl u03b2 d glucosaminide cpr nag used in the present invention can readily be prepared from 3 3 39 dichlorophenolsulfonphthalein cpr and 1 chloro 1 deoxy 2 3 4 6 tetraacetyl u03b1 d glucosamine according to the process disclosed in kokai 58 994 unlike cnp nag the aforementioned cpr nag is freely and quickly soluble in water and therefore no specific additives such as surfactants are needed accordingly substrate solutions can be prepared very quickly it is very important to stabilize substrates because decomposition of them makes the measurable limitation of enzyme activities narrower cpr nag used in the present invention is fairly stable even in the absence of any stabilizers and therefore it may be formulated as it is further it can be stored in a refrigerator for a long period of time without decreasing the measurable limitation borax may be added to it as a stabilizer if much longer.