Demyelination was induced in the superior cerebellar peduncles of weanling mice by the administration of Cuprizone. Remyelination occurred when the animals were replaced on a normal diet. Perineuronal satellite oligodendrocytes in the periventricular gray were clearly seen to be remyelinating axons. This study demonstrates for the first time the role of these cells in remyelination, and raises the possibility that they may be involved in normal myelination of the central nervous system.