The mechanism of the GN induced by the intravenous injection of antibodies directed against renal tubular epithelial antigens (RTE) was studied by the use of antibody specifically purified by affinity chromatography. With this reagent RTE antigens could be demonstrated on frozen sections of glomeruli as well as on glomerular cells in culture. The antibodies were radiolabelled, and using paired label techniques glomerular binding could be measured in vivo. In normal rats, approximately 4% of the antibody injected was specifically bound in the glomeruli. Binding was not detectable on proximal tubular brush borders. In rats treated with 100 mg/kg of aminonucleoside of puromycin, a substance known to induce alterations of glomerular epithelial cells, it could be shown that glomerular binding was selectively decreased. These observations indicate that immune deposits in passive Heyman nephitis are formed mainly in situ and that local alteration of the glomerulus can markedly influence deposit formation.