With a casuistics (multiple myoma with IgD-paraproteinaemia in a 64-year-old woman) some problems in the diagnostics of the rare paraproteins in plasmocytoma are described summarizing. In the case demonstrated with much accelerated BSR, dysproteinaemia and clear M-gradient in the pherogram as well as a deminution of IgG, IgA and IgM in the serum the IgD-paraprotein with multivalent antisera could not be proved; this was possible only with monospecific anti-IgD-serum.