The recent elucidation of the structure of immunoglobulins, and the more precise immunologic and chemical characterization of the proteins produced by patients with proliferative disorders of plasma cells and lymphocytes have led to a clearer understanding of the biosynthetic alterations accompanying them. Consequently, these disorders are now frequently classified on the basis of the products of the neoplastic cells. Thus, multiple myeloma is now defined by the type of proteins produced (G,A,D and E myeloma), and the biosynthetic processes in myeloma and macroglobulinemia are described either as balanced synthesis of heavy (H) and light (L) chains resulting in only a . . .