In order to prevent the development of essential fatty acid deficiency, 19 premature babies and term infants needing parenteral nutrition were studied during 14 days. Intralipid 20% was administered to ten and sunflower seed oil was rubbed six times daily on the skin of nine infants. Fatty acid pattern of plasma lipids were determined at birth and days 7 and 14. Levels of C16:0, C18:1, C18:2, and C20:4 did not change in the Intralipid group. In the sunflower seed oil group a decrease in C18:2 developed, which could be corrected by administering Intralipid (Intralipid was administered to four patients who had previously received sunflower seed oil during 14 days). Although Intralipid administration is often controversial or contraindicated in premature infants (hypoxia, septicemia, acidemia), it appears necessary to prevent plasmatic deficiency in C18:2. The latter cannot be prevented by topical application of sunflower seed oil, not even in very low birthweight infants.