Light and transmission electron microscopic studies as well as immunohistochemical investigations were performed on a case of multiple myeloma in a 40-year-old female with systemic kappa light chain deposition. The latter took the form of extensive deposits in the liver, spleen and bone marrow. Amyloid was not found in these deposits, although it was present in the wall of branches of the portal vein. Conversely, amyloid but not light chain deposition was found in the tongue, synovial membrane from the knee and myocardium. The kidney was the only organ to show both amyloid and light chain deposits intimately associated with each other in and around tubules and collecting ducts. Ultrastructurally the light chain deposits were seen to be biphasic, having two granular components of different electron density. In the spleen and bone marrow, but not in the liver, the kappa light chain deposits were surrounded by multinucleated giant cells. This is the first report of light chain deposition disease associated with a foreign body type of giant cell reaction. The morphological variability of organ involvement suggests that the molecular structure and conformation of the deposited light chains are heterogeneous and may reflect a broad spectrum of metabolism of these deposits in various organs.