Oligodendrocyte progenitor CG4 cells were labeled with bisbenzimide and transplanted in the lumbar spinal cord of rats 15 to 17 days prior to the induction of experimental autoimmune encephalomyelitis (EAE). EAE was induced by immunization with the encephalitogenic peptide of myelin basic protein (amino acids 68-88; C1) in adjuvant, either alone or in combination with a single injection of an anti-myelin oligodendrocyte glycoprotein (MOG) antibody to enhance central nervous system (CNS) demyelination. In control animals without EAE, the survival and migration capacity of CG4 cells was minimal. In striking contrast, both the survival and migration of this oligodendrocyte progenitor cell line were greatly enhanced in animals with EAE. In both disease models, large number of CG4 cells were still found in the spinal cord 50 days after transplantation, by which time they had migrated up to 6 cm from the transplantation site. Migrating CG4 cells were found in the subpial space, around the ependyma and blood vessels, and as well as in the grey and white matter of the CNS parenchyma. In all these locations, the CG4 cells were often associated with reactive astrocytes. These data strongly support the concept that inflammatory responses within the CNS promote, rather than inhibit, the survival and migration of transplanted oligodendrocyte progenitors in the adult CNS.