A 69-year old man of Bence Jones (λ) type plasmacytoma is described, who showed numerous virus-like particles electronmicroscopically in his myeloma cells; 5% of the myeloma cells of bone marrow contained round shaped inclusion bodies of 0.5∼5 μ in diameter, in which numerous virus-like particles of 40∼90 mμ in diameter were seen. Inclusions and particles were surrounded by a unit membrane, which was about 90 Å thick and could be resolved into a triple-layered structure. The particles were located along periphery of, or scattered in the inclusions. Occasionally they were found in endoplasmic reticulums.
Though they superficially resembled A-particles, they did not possess double membrane and were not as uniform in size as A particles. Buddings or releasing out of the particles from cells, B-particles, and C-particles, were not found.
These observations suggest that they are probably not viruses. They may be closely related to Golgi vesicles, because in this case Golgi vesicles were well developed, inclusions existed near Golgi area, and the pictures which suggested transition from Golgi vesicles to the particles were often recognized.
