Clinical findings and structural alterations in the kidneys of 6 patients with sarcoidosis and an associated glomerulonephritis are described. Five of the 6 patients manifested the nephrotic syndrome during some phase of their illness. Additional clinical evidence of renal disease included persistent microscopic hematuria (5 patients), hypertension (4 patients) and progressive renal failure (3 patients). Glomerular pathology varied and included proliferative glomerulonephritis (3 patients), membranous glomerulonephritis (1 patient), and chronic glomerulonephritis (2 patients). In 2 patients sequential examination of the kidney was possible, with renal biopsies preceding autopsy examination by 3 and 6 years, respectively. Glomerular pathology had progressed in severity in each case. Immunofluorescent studies in 2 patients revealed patterns of glomerular antibody localization consistent with immune complex disease. Electron microscopic studies of 1 revealed membranous changes characterized by electron-dense subepithelial and intramembranous deposits. Totally unexpected were virus-like intraendothelial structures in the glomeruli identical to those previously reported in systemic lupus erythematosus. Since current evidence suggests that the pathogenesis of both membranous and proliferative types of glomerulonephritis is immunologic, it should not be surprising that sarcoidosis, a disease which quite possibly results from an immune response to a disseminated antigen(s), should occasionally include glomerulonephritis as a part of its histologic expression.