The vicissitude of the anti-kidney antibody was mainly observed on the cases of experimental nephritis in tabbit by the methode of Masugi's nephritis and kidney homosensitization, and the significance of its antibody and the movement of its antibody into urine were also studied. And the following results were obtained. 1. The slight elevation of the kidney auto-antibody was observed in all cases of Masugi's nephritis and the elevation of its antibody was observed since the 5th or 7th day after the injection of nephrotoxin and the persistence of the elevated antibody titer (1:4~1:8) was observed until one month later. 2. The correlation between the appeance of the kidney auto-antibody in peripheral blood in Masugi's nephritis and the various clinical findings or histological changes in kidney was relatively observed. 3. The elevation of the kidney homo-antibody was observed in all cases with the homo-sensitization by the kidney emulsion adding adjuvant, after 17 or 24 days and the occurrence of nephritis was even slightly observed in half of them, comparing with Masugi's nephritis. 4. In the above cases of experimental nephritis, the decrease of complement value was observed in accordance with the appearance of the anti-kidney antibody (kidney auto-or homo-antibody). 5. The movement of the kidney auto-antibody into urine was observed, and the correlation between the above phenomenon and the fall of the Albumin-Globulin ratio in urinary protein or the increase of the γ-globulin fraction was also observed. 6. Since the above results, the participation of the anti-kidney antibody (kidney auto-or homo-antibody) was clear for the development of the above experimental nephritis. And it was thought that the participation of its antibody could not be disregarded for the appearance of the pathological change in the kidney since there was the close correlation between the appearance of the anti-kidney antibody and the fall of the complement titer or the appearance of renal symptom.