The distribution of rabbit antirat tubular antigen antibody (ATAb) in rat kidneys was examined by immunofluorescence at various times after the intravenous injections of various doses. The results were also compared with those of the experiments in rats made already nephrotic by aminonucleoside of Puromycin. Our results that ATAb could be demonstrated not only in the glomerular capillary wall but in the brush border of the proximal tubule might suggest the possibility that the tubule could also be damaged by immunological mechanism, although no histological support could be obtained. In the patients of the chronic glomerulonephritis (membranous glomerulonephritis), some of which are considered to be caused by tubular antigen and anti-tubular antigen antibody complexes, more attention should be attracted not only to the pathological changes in glomerulus but to those in proximal tubule.