Present experiment was performed in order to establish the optimal reaction conditions for determination of urinary AAP and GRS activities and to investigate the applicability of urinary AAP and GRS in nephrotoxicity test in rat. The results were as follows ; 1. The optimal pH of phosphate buffer for determination of urinary AAP activity was 7.8. 2. The Michaelis constant of urinary AAP ranged from 0.8 to 1.0mmol/$ell$ 3. The optimal wave length for determination of urinary GRS activity was 405nm. 4. The optimal pH of acetate buffer for determination of urinary GRS activity was 5.6. 5. The Michaelis constant of urinary GRS ranged from 0.65~0.79mmo1/$ell$. 6. The AAP activities in gel-filtered samples were significantly higher than those in crude samples. Mean values of AAP activities in gel-filtered samples and crude samples were 29$pm$20 and 20$pm$13U/$ell$, respectively. 7. There was not significant difference between gel-filtered samples and crude samples in urinary GRS activities. Mean values of GRS activities in gel-filtered samples and crude samples were 57$pm$40 and 56$pm$39U/$ell$, respectively. 8. Limits of linearity of urinary AAP and GRS activities were 2.0 and 3.6U/$ell$, respectively. 9. Within-run imprecisions of the assays, were acceptable, as the coefficients of the AAP activities ranged from 5.5 to 6.3% and those of GRS activities ranged from 1.4 to 6.2%, respectively. 10. Urinary AAP excretion was 675$pm$227mu/24hrs.kg before administration of potassium dichromate, and increased significantly to 4246$pm$2567mU/24hrs.kg within 24 hours after administration of potassium dichromate. 11. Urinary GRS excretion did not increase significantly after administration of potassim dichromate. 12. From these findings it is concluded that urinary AAP excretion is early and sensitive Indicator to detect kidney damage in nephrotoxicity experiment.