Osteocytes were isolated from bones of dinosaur, Tarbosaurus bataar, aged approximately 80 million years. About 10% of sections of such osteocytes revealed the presence of DNA, the latter being demonstrated histochemically using Feulgen's method and staining with ethidium bromide. An attempt was made to explain why DNA remnants could be detected only in sectioned osteocytes which all originated from bones of two (out of ten) specimens. Scanning electron micrographs showed that while in the majority of osteocytes the metaloorganic sheath developed during fossilization was damaged and porous, in some it was well preserved and intact. It is suggested that an intact cell sheath enabled the preservation of DNA, though it simultaneously prevented the penetration of reagents and dyes into the cells in unsectioned material. In osteocytes with porous sheaths, the preservation of nucleic acids until today would not be possible.