The effects of psychosine on the metabolism of myelin associated glycolipids such as galactocerebroside and sulfatide in mouse brain cell cultures were investigated in order to clarify the mechanism of demyelination in globoid cell leukodystrophy (Krabbe's disease). The incorporation of 3H-galactose into cerebroside and sulfatide was studied in the presence of psychosine (1-3 micrograms/ml medium). These data indicated that psychosine inhibited the incorporation of 3H-galactose into cerebroside and sulfatide not in astroglial cell culture but in oligodendroglial cell culture. Oligodendrocytes produce myelin in the central nervous system, and cerebroside and sulfatide are major components of myelin. These results suggest that psychosine influences the lipid metabolisms of myelin and subsequently leads to the demyelination in Krabbe's disease.