To determine the relative role of malabsorption as the cause of decreased linoleic acid in blood and tissue lipids of patients with cystic fibrosis (CF) and pancreatic insufficiency, the increase in plasma linoleic acid was determined after ingestion of various lipid supplements. CF patients with documented pancreatic insufficiency and normal control subjects were given each of four different lipid supplements on separate days (a minimum of 3 days apart). The supplements were commercial safflower oil, Microlipid, Captex 810D, and Captex 810B. Fasting subjects consumed 36 g of lipid in a milk shake containing 15 g of protein and 45 g of carbohydrate. Plasma samples obtained at 0, 2, 4, 6, and 8 h after the meal showed that CF patients absorbed linoleic acid from all of the lipid preparations tested when administered with their regular dose of pancreatic enzyme supplement. The mean maximal increase in percent plasma linoleic acid in CF patients was not different from controls after ingestion of safflower oil, Microlipid, and Captex 810B. With Captex 810D the CF patients had a significantly higher increase in percent plasma linoleic acid than controls, 6.75% vs. 2.27%, respectively, at 2 h (p < 0.01), and 11.10% vs. 4.65% at 8 h(p < 0.01). The CF patients also appeared to absorb the Captex products faster than controls, suggesting that presence of medium chain length fatty acids in these structured lipids facilitated their utilization by CF patients. The results indicate that malab-sorption alone cannot account for the inadequate or marginal essential fatty acid status of CF patients. The fact that linoleic acid was absorbed as well by CF patients as controls in the present study suggests that CF patients in many previous supplementation studies either have not been given sufficient linoleic acid or have used the linoleic acid ingested to meet caloric needs. There is increasing evidence that adequate total caloric intake may be a far more important factor in determining the essential fatty acid status of CF patients than previously recognized. Our results suggest that long-term consumption of supplemental linoleic acid in addition to adequate caloric intake should improve the linoleic acid status of most, if not all, CF patients.