Using radioimmunoassays (RIA) for the myelin specific proteins, myelin proteolipid protein (PLP) and myelin basic protein (MBP) and an enzyme assay for the activity of the myelin marker enzyme 2'3' cyclic-3' phosphohydrolase (CNPase), we have studied plaque, periplaque and normal appearing white matter (NAWM) tissue. We found that all three mylein proteins are decreased in all regions, including NAWM, of MS brain, with a decreasing gradient from NAWM to perregion. Surprisingly, when the ratios of the proteins were calculated, MBP activity, although decreased was found to be relatively preserved.