Nuclei of human neurilemoma cells exhibit deep and extensive invaginations of part of their surface. Such invaginations contain cytoplasmic matter. However, in areas of the nucleoplasm distant from the invaginations, small membrane-bound bodies, some of which contain a "nucleoid," occur either singly or grouped together and enclosed within a large membrane body. These small bodies are not considered virus-like. Degenerated nuclei from cultured tumor tissue contain spherical bodies, 130 to 230 nm in diameter, with spikes on their surface similar to those seen on envelopes of herpes-type viruses. Significance of these bodies in vivo and in vitro tumor tissues is not known.