Although more than 100 years have elapsed since Richard Bright's classic description of a group of nonsuppurative renal diseases, neither our understanding of the etiology and pathogenesis nor the methods of treatment for these diseases have improved appreciably. With concepts presently available the clinician faced with a patient suffering from a chronic renal disease finds diagnostic criteria, classification, basis for prognosis, and method of treatment completely inadequate. For example: Are acute and chronic glomerulonephritis the same disease, and, if not, how are the etiologic and pathogenic mechanisms of the two diseases related or different? Where in the spectrum of renal disease is the nephrotic syndrome properly assigned? Is anaphylactoid purpura with nephritis a form of acute glomerulonephritis, as some have proposed, or does this syndrome belong in the group of diffuse vascular diseases of which disseminated lupus erythematosus and polyarteritis nodosa are examples? In an attempt to gain information regarding