A micromethod for the investigation of the fatty acid composition of sphingomyelin in presented. In the cerebral white matter of 17 normal adult brains, analyzed for reference, the predominant fatty acids are C 18:0 and C 24:1. Our results are in agreement with those of other authors. Short chained fatty acids are relatively increased in young children; this shift is typical of "immature" myelin. Similar changes are described here in old persons and cases of non-specific brain damage associated with demyelination (autolysis, chronic uremia, juvenile chorea). Sphingomyelin fatty acid composition can be considered a sensitive measure of both disturbed myelination and demyelination.