The survival of the embryonal, neonatal and mature neurons from the spinal ganglia under the condition of iso- and allotransplantation into the colon mesentery of the rat was studied in chronic experiments. For seven months one-third of the mature neurons, about 100% of the neonatal neurons and only 5% of the embryonal neurons survived. The survived neurons had a pseudounipolar form and their initial glomeruli had excessive overgrowth in the form of perivascular plexus. These regenerating nerve fibres together with growth cones make terminals in the form of buds, rings and loops. Myelinization of the regenerating nerve fibres at ultrastructural level was studied.