Bone marrow samples of 97 patients with multiple myeloma were examined ultrastructurally over a period of eight years, and the degree of nucleo-cytoplasmic maturation asynchrony (NCA) of myeloma plasmocytes was estimated according to the classification scale of Graham and Bernier. One half of the patients showed first degree, 40 percent second and 10 percent third degree of NCA. Clinical classification of the disease according to the staging system of Durie and Salmon and the quantitative staging system of Salmon and Wampler showed some relation to the degree of NCA. The degree of NCA was found to be related to the density of the bone marrow infiltration with myeloma plasmocytes but not to the response to chemotherapy. Some relation was seen to exist between the degree of NCA in myeloma plasmocytes at diagnosis and the prognosis of the disease. The role of electron microscopical analysis in MM diagnostics and its contribution to management of the disease are discussed.