We report three patients, from two unrelated families, with anti-tubular basement membrane (TBM) antibody nephritis associated with membranous nephropathy. This rare disorder is characterized by nephrotic syndrome, tubular dysfunction, and progression to renal failure. Direct immunofluorescent studies in these patients revealed linear IgG deposition along the proximal TBM, while circulating antibodies reacting with proximal TBM but not with glomerular basement membrane were identified by indirect immunofluorescence. Sera from all three patients reacted by enzyme-linked immunosorbent assay and Western immunoblotting with purified 58-kd tubulointerstitial nephritis (TIN) antigen isolated from TBM. Additional reactivity with a 175-kd component, which may be a higher-molecular-weight form of TIN antigen, was observed by immunoblotting. Since recurrent Fanconi syndrome was seen after transplantation in one patient, anti-TBM antibodies were removed by plasmapheresis prior to kidney transplantation in the other two patients. Neither patient has clinical evidence of recurrent anti-TBM nephritis in the allograft despite the post-transplantation reappearance of anti-TBM antibodies in the serum of one patient. Serologic and molecular HLA class I and class II polymorphism analysis has identified the presence of both HLA-B7 and -DRw8 antigens in two unrelated affected individuals (0.3% expected frequency in the white population). We conclude that sera from patients with anti-TBM nephritis associated with membranous nephropathy react with 58-kd TIN antigen previously implicated in the pathogenesis of primary anti-TBM nephritis. This rare autoimmune disorder may be HLA associated with B7 and/or DRw8, providing susceptibility to the disease. Further investigation is needed to understand the pathogenesis of recurrent anti-TBM nephritis in the renal allograft.