We found a small but statistically significant reduction in the linoleic acid concentration of white blood cells and platelets in MS patients. The percent linoleic acid concentration (mean +/- S.D.) in the white blood cells if 24 MS patients was 8.8 +/- 1.8% as compared with 11.4 +/- 4.9 in 24 age and sex-matched controls (p less than 0.05). Platelet levels were 8.5 +/- 2.4% and 10.6 +/- 3.8% respectively (P less than 0.05). Serum linoleic acid levels were not significantly different in the two groups. The possible role of linoleic acid in the pathogenesis of MS has yet to be defined.