Duodenal ulcer is associated with low dietary linoleic acid intake. It has been suggested that the falling incidence and virulence of duodenal ulcer is related to increased dietary polyunsaturated essential fatty acid intake. The adipose fatty acid profile, which closely reflects dietary intake, was measured in 35 men with chronic duodenal ulcer and 35 matched control men. The mean percentage of linoleic acid in adipose tissue was significantly lower in the ulcer group (10.0 (0.7) v 12.3 (0.7)%, p less than 0.01) and this difference was found in both smokers and non-smokers. This finding suggests that the diets of duodenal ulcer patients are deficient in linoleic acid and this could be of aetiological importance. 