The effect of essential fatty acid (EFA) deficiency on the lipid composition of basolateral plasma membranes (BPM) from intestinal mucosal cells was investigated in weaning pigs fed control or EFA-deficient diets for 12 weeks. The phospholipid and cholesterol contents relative to protein were similar in both groups, showing a cholesterol/phospholipid molar ratio of 0.6. The distribution of phospholipid classes was also unaffected by the diet. In contrast, fatty acid profiles of the two phospholipid main classes, phosphatidylcholine and phosphatidyl-ethanolamine were altered by EFA deficiency. Linoleic acid (18:2n-6) was largely reduced, whereas arachidonic acid (20:4n-6) only slightly decreased in EFA-deficient pigs. The unsaturation index was essentially maintained by high levels of oleic acid (18:1n-9) and by conversion of oleic acid to 5,8,11-eicosatrienoic acid (20:3n-9). Finally, during the period of EFA deficiency, the lipid composition of BPM of the intestinal mucosal cells was little affected, suggesting a preferential uptake of 20:4n-6 and (or) precursor mobilized from other tissues. However, an effect of dietary treatment on the function of membrane-associated proteins cannot be ruled out.