Quantitative determinations were made of the main lipid classes in CSF samples of normal males and of chronic alcoholics after acute abuse, and after 14 days' treatment. The fatty acid profiles of cholesteryl esters, trigly cerides, choline and ethanolamine phosphoglycerides were compared with those of corresponding serum samples. The most constant difference found between serum and CSF was the lower concentration of linoleic acid (18:2) in CSF, which was most pronounced for the two phosphoglycerides. The fatty acid profile of CSF from normals and alcoholics differed only regarding these two lipids.