Abstract
—Proteolipids isolated from rat cerebral cortex have unesterified fatty acids associated with them. The fatty acids may be divided into two pools on the basis of their susceptibility to methylation by diazomethane. The fatty acid composition of the two pools is different. Proteolipid fractions separated by chromatography on Sephadex LH 20 have varying amounts of unesterified fatty acids associated with them and the composition of the fatty acids is different for each proteolipid fraction.