Quantitative assay of Igs in the saliva of patients with IgA or IgG multiple myeloma or Waldenström’s IgM macroglobulinemia revealed that only minute quantities of these monoclonal Igs, traced by their idiotypic determinants, reached the saliva (~1% of each isotype present) despite their presence at very high concentration in plasma, and despite the ability of pIgA to bind to pIgR in vitro (33). This evidence concerns the gene CUBN and plasma cell myeloma.