The linoleic acid intake of patients with multiple sclerosis is not significantly different from that of healthy control subjects. This is true both in absolute terms and when linoleic acid intake is expressed as a percentage of total fat intake. In the other categories of illness, included as control groups, linoleic acid intake was significantly decreased only in patients with acute non-neurological illness and in this case only when considered in absolute terms. In all groups studied the daily linoleic acid intake was in excess of 1·7% of the total calorie intake and in the case of multiple sclerosis was 2·7% of the total calories ingested. Since other workers have shown that linoleic acid absorption is not altered in multiple sclerosis and we have shown that the diet is not deficient, it seems that the decrease in linoleic acid content is due to some process occurring after the absorption of this essential fatty acid.