Proteolipid protein, the major protein component of central nervous system (CNS) myelin, is known to contain approximately 2% by weight of covalently bound fatty acids. Recently, this protein was also found, though at a lower concentration, in the peripheral nervous system (PNS). The present study was undertaken to determine whether PNS proteolipid protein, like its CNS counterpart, was fatty acylated. Myelin PLP and DM-20, the two proteins that constitute the proteolipid protein fraction, were isolated from bovine sciatic nerves by chromatography on a methylated Sephadex G-100 column. The identity of the isolated proteins was determined by (a) SDS-PAGE, (b) Western blot analysis, and (c) amino acid analysis, and fractions containing only PLP and DM-20 were subjected to acid-methanolysis. Gas-liquid chromatography of the released methyl esters revealed the presence of fatty acids (2.9% w/w) distributed as approximately 47% palmitic, 22% stearic, and 19% oleic acid. Similar results were obtained for bovine white matter proteolipid protein when isolated and analyzed in parallel with the peripheral nerve protein. These data unequivocally demonstrate that both PNS and CNS proteolipid protein are equally acylated.