Ten normotensive subjects had their omnivore diet supplemented with increasing doses of linoleic acid in the form of safflower seed oil in order to examine the effects of this polyunsaturated fat upon leucocyte sodium transport. Increasing the dose ingested to the limits of tolerance produced a significant decrease in ouabain resistant sodium efflux (P less than 0.05) but no significant change in total or ouabain-sensitive sodium extrusion. Intraleucocytic sodium content was correlated with erythrocyte membrane oleic acid % (r = 0.368, P less than 0.05); leucocyte ouabain resistant flux was correlated with oleic acid % (r = 0.453, P less than 0.01) and linoleic acid % (r = -0.319, P less than 0.05). No such associations were observed with ouabain sensitive sodium extrusion. No changes in body weight or urinary electrolyte excretion were observed. It is concluded that, at physiological concentrations, membrane linoleic acid content influences transmembrane sodium fluxes but not through modulation of sodium pump activity. Furthermore, the beneficial effect of this dietary manoeuvre, observed previously with small increments of safflower seed oil, was not seen in this experiment so the hypotensive activity of this manipulation must be regarded as limited.