Morphological investigation of transplants of the rat 14-15 d embryonal neocortical and spinal anlages after long term transplantation into the adult animal sciatic nerve was conducted. Transplants were shown to retain viability on 19th month postoperatively, with the part of neurons demonstrating dystrophic changes and death. Neocortical neurons were shown to preserve higher viability in sciatic transplants. Increase in number of neurons showing irreversible changes correlates well with the development of degenerative changes in blood vessels, their calcification and formation of psammoma-like bodies.