Several distinct stages of differentiation have been described for the oligodendroglial lineage in vitro (Gard and Pfeiffer, 1990 ; Gard et al., 1995 ). These include the actively proliferating bipolar or tripolar oligodendroglial precursor cell, characterized by the presence of GQ1c and GD3 gan-gliosides in the plasmalemma. The oligodendroglial precursor cell differentiates into the multipo-lar oligodendroblast, a proliferative cell that has sulfatide, but no galactocerebroside, in its plasma-lemma. The oligodendroblast differentiates into the mitotically quiescent oligodendrocyte, a cell characterized by the presence of galactocerebroside in its plasmalemma. These oligodendrocytes also express other myelin-associated proteins, such as myelin basic protein. When transplanted into the central nervous system (CNS) of hypomyelinating hosts, oligodendrocyte precursors migrate over considerable distances, and give rise to large numbers of myelinating oligodendrocytes; oligodendroblasts migrate only short distances, and give rise to far fewer myelinating oligodendrocytes (Warrington et al., 1993 ). When transplanted into the CNS, the mature oligodendrocyte will also myelinate axons (Duncan et al., 1992 ).