The study of monoclonal immunoglobulin-associated nephropathies is useful for analyzing the physicochemical properties of immunoglobulin components responsible for their deposition in the kidney. Notable advances include the first description of truncated heavy-chain deposition disease, characterization of protease resistance and binding properties of immunoglobulin light chains involved in myeloma-associated Fanconi's syndrome and cast nephropathy, and identification of hepatitis C virus as a plausible causative agent of the so-called essential mixed cryoglobulinemias.