The ultrastructural localization of immunoglobulins (Igs) in immunologically mediated glomerulonephritis was achieved in ultrathin sections of glutaraldehyde-fixed, post-osmicated, Epon-embedded human renal needle biopsies using the indirect immunogold staining procedure. Extracellular Igs were identified in electron-dense deposits in subendothelial, intramembranous, subepithelial and mesangial locations in different cases of immune-complex-mediated glomerulonephritis. The excellent preservation of the ultrastructural morphology of the tissue sections made it possible to precisely correlate the presence and distribution of the antigens with those of the electron-dense deposits, which are the ultrastructural hallmarks of these diseases. Our post-embedding staining procedure which allows extracellular Igs to the accurately localized should be a very useful tool for immunomorphological investigations of glomerulonephritis.