In order to evaluate the incidence of extraglomerular immunoglobulin deposits and to correlate their presence with histopathologic abnormalities, we performed both prospective and retrospective immunofluorescence studies of renal biopsy specimens. Of 200 diagnostic biopsy specimens examined prospectively, 21 had extraglomerular deposits, 19 in association with presumed immunologically-mediated glomerulonephritis. Nine had linear immunoglobulin deposits on tubular basement membrane (antitubular basement membrane antibodies), in one case coexisting with granular deposits, and 13 had granular deposits on tubular basement membrane, in peritubular capillaries and/or arteries, or in tubular cytoplasm (probably immune complexes). Linear deposits on tubular basement membrane were usually associated with antiglomerular basement membrane nephritis or methicillin-associated interstitial nephritis; granular extraflomerular deposits were seen primarily in systemic lupus erythematosus, cryoglobulinemia or membranoproliferative glomerulonephritis.. The incidence of immunoglobulin deposits was high in the three groups of patients examined retrospectively being present in 37 or 47 patients with antiglomerular basement membrane mephritis, 22 or 32 patients with systemic lupus erythematosus of 24 of 130 renal allograft recipients. The contribution of antitubular basement membrane antibodies to renal damage was difficult to assess, although studies in experimental animals attest to their pathogenicity. The occurrence of granular extraglomerular deposits appeared to correlate roughly with the degree of tubulointerstitial injury in the patients with systemic lupus erythematosus.