Analysis of phospholipids (PL), cholesterol esters, triglycerides (TG), and free fatty acids (FFA) was performed on plasma and RBCs in two sick low-birth-weight infants who received total parenteral nutrition including Intralipid for the first 9 and 12 weeks of life, respectively. There was an increase in the total concentration of the plasma IG and FFA in the infants receiving Intralipid as compared with controls. These elevated lipid levels were not detected by visual inspection of the plasma. When compared with control infants, higher levels of linoleic acid were found in the plasma and RBCs of infants receiving Intralipid while plasma PL contained less arachidonate. Histological examination of the lung in both infants who received Intralipid revealed numerous globules of sudanophilic material in alveolar macrophages and capillaries. There is a possibility that prolonged administration of Intralipid may be associated with altered pulmonary and reticuloendothelial system function.