The paper describes a case of diagnosis of the rare monoclonal secretion-associated disease crystalline histiocytosis with kidney and bone marrow involvement. The female patient with multiple myeloma (MM) was found to have intralysosomal crystals in the cells of the bone marrow (histiocytes, plasmocytes), kidneys proper (mesangiocytes, podocytes), and subsequently in those of a kidney graft. Lower secreted monoclonal IgG and ceased Bence-Jones protein secretion after MM chemotherapy were accompanied by improved and stabilized kidney graft function. However, a repeat morphological study of a renal biopsy specimen showed that the crystalline inclusions were preserved in the podocytes. By comparing the immunological and renal responses, it is reasonable to suggest that monoclonal IgG rather than Bence-Jones protein is of value in the pathogenesis of crystal formation.