In relation to the renal changes in the "collagen disease", an experiment was carried out to clarify the pathogenetic mechanism of the so-called "lupus nephritis" by means of the provocation of the active anaphylaxis in the kidney of the rabbit sensitized with bovine serum gamma globulin. Based upon the Hamamoto's theory of "Intravascular Antigen-Antibody Reaction", the bovine gamma globulin solution was injected directly through the renal artery into the kidney of the rabbit whose serum titer against the bovine gamma globulin was sufficiently high. Rabbits were sacrificed from one day to twenty days after the provocative injection, and then the pathohistological changes of the kidney were examined. Major pathohistological changes of the kidney were as follows: 1) Dramatic exsudative and necrotizing inflammatory changes of the glomerular capillaries in early stage, 2) Thickening of the capillary basement membranes which were often irregular, 3) Lesion of the proliferative glomerulonephritis 4) Glomerular fibrosis and glomerular cicatrization 5) Hyaline droplet degeneration of the tubuli 6) Desquamation of the tubular epithelial cells 7) Necrotizing arteritis in small arteries 8) Perivascular infiltration of monohistiocytes and leucocytes 9) Proliferation and degeneration of endothelial cells of capillaries and arteries. These pathohistological changes resembled the renal changes in systemic lupus erythematosus which stand for "collagen disease". These observation indicate that the renal changes in collagen disease may be of "allergic" mechanisms.