Hereditary nephritis (HN) is associated with antigenically abnormal glomerular basement membrane (GBM) manifest by reduced or absent binding of MCA-P1, a mouse monoclonal antibody which recognizes Goodpasture antigen. In the present studies, immunoblotting has been used to analyze antigenic and biochemical composition of renal tissue from patients with HN in whom binding of MCA-P1 could not be demonstrated by indirect immunofluorescence (IIF). Pooled normal collagenase-solubilized GBM (CS-GBM) and CS-GBM from three patients with either end-stage renal failure (ESK1-3) or HN (HNK1-3), were examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis gel and, after transfer by Western blotting to nitrocellulose, reacted with sera from six patients with anti-GBM disease (GPS1-6) or anti-GBM antibody containing sera from three transplanted HN patients (HNS1-3), different from those patients with HN contributing HNK1-3. We found that GPS1-6 and HNS1-2 recognized the same six major bands in CS-GBM and ESK1-3 (between 54 and 24 kilodalton (kd) but only three bands (48, 42 and 24 kd) in HNK1-3. HNS3 only bound strongly to bands of 54 and 26 kd in CS-GBM or ESK1-3 and not all to HNK1-3. Immunoblotting studies of HNK1-3 have shown a partial rather than absolute loss of Goodpasture antigenicity (54, 28 and 26 kd bands). Studies with HNS1-3 suggest heterogeneity of antibody responses to allografted kidneys between patients with HN; HNS-3 showed restricted antibody specificity with recognition in CS-GBM of some bands antigenically absent from HN kidney. The abnormality in HN kidneys appears closely related to, but distinct from, the Goodpasture determinant and the inherited defect in HN may involve an essential modifying enzyme.