• A chemical-pathologic study of globoid leukodystrophy (GLD) was made that compared myelin isolated from maximally involved central white matter with myelin from noninvolved U fiber areas. The results were compared to analyses of myelin from normal, age-matched control human brains. Myelin from U fiber areas contained relatively greater amounts of a lighter myelin fraction and this lighter myelin differed in protein and lipid composition from the heavier myelin fraction. The data have been interpreted to suggest that the metabolic error in GLD results in the formation of an unstable compact or heavier myelin and that a subsequent process of disintegration selectively affects this component.