Over the last decade, glial cell transplantation has become a firmly established experimental technique with which to study the biology of glial cells in CNS repair. Using this technique, it has been possible to relate in vitro observations on the developmental, migratory and myelinogenic properties of the oligodendrocyte lineage to in vivo situations that are relevant to the repair of myelin-deficient environments in adult mammals. It has also revealed the complex nature of the interactions that occur between demyelinated axons and glial cells of both the central and peripheral nervous systems. The progress that has been made in this field thus far has done much to encourage the view that therapeutic strategies based on glial cell transplantation could be developed within the near future.