In a randomised double blind study to determine whether an increase in the polyunsaturated fat linoleic acid might influence leucocyte membrane sodium transport 22 normotensive volunteers received an oral supplement of linoleic acid or placebo daily for four weeks. Mean total sodium efflux rose significantly during supplementation with linoleic acid compared with placebo. In addition, all components of lying and standing blood pressure fell, though only the fall in supine systolic pressure was significant. Dietary supplementation with linoleic acid may alter ion fluxes across the cell membrane, presumably through changes in its physicochemical structure. In addition, the change in fat intake may lower blood pressure, though to only a very modest extent.