At the autopsy of a 68 year old man with plasmacytoma of the lambda light chain type we found polygonal interstitial cells with unusual crystalline inclusions, which were not readily identifiable and slightly resembled Leydig cells in conventional microscopy. In electron microscopy these could be identified as plasmacytoma cells, representing a testicular involvement. Comparable cells could be shown in the bone marrow. In immunochemistry we found a polyclonal reaction for lambda light chains suggesting a similar phenomenon as the so-called Russell bodies. As far as we know the literature, this finding in a testicular metastasis has not been described.