One hundred and sixteen patients with acute remitting multiple sclerosis (MS) took part in a double-blind controlled trial of treatment with polyunsaturated fatty acids and were randomly allocated to one of four groups. Two groups received linoleic acid, one alone as a spread and one with gamma-linolenic acid in capsules (Naudicelle); and two control groups received oleic acid, one as a spread and one in capsules. Rates of clinical deterioration and frequencies of attacks were not significantly different between treated and control groups. Exacerbations were shorter and less severe in patients receiving a high dose of linoleic acid than in controls, but those receiving a lower dose--that is, Naudicelle--showed no such difference. Thus supplementing the diet with 20 g linoleic acid marginally affected the duration and severity of relapses of MS but had no effect on overall disability. The dose of Naudicelle used provided insufficient supplementation.