Injection of a suspension of embryonic rat central nervous system (CNS) cells into an area of persistent demyelination, produced in the cat spinal cord by injecting ethidium bromide into an area previously exposed to 40 Grays of x-irradiation, results, initially, in Schwann cell remyelination of the demyelinated axons. However, the Schwann cells are subsequently rejected; a response which confirms that the remyelinating cells are of rat origin.