Previous histochemical studies of iron in the brain demonstrated iron enrichment in oligodendrocytes, but the iron-enriched oligodendrocytes had a spatially restricted distribution that excluded major white matter tracts. In this study we used techniques designed to permeabilize tissue, combined with iron histochemistry, and we observed iron-enriched oligodendrocytes in regions previously thought to lack such cells. Our data suggest that most, if not all, oligodendrocytes are enriched in iron. We suggest that iron functions in the formation and/or maintenance of the myelin sheet and may play a role in the pathology of myelin diseases.