The purpose of this study was to follow the long-chain polyunsaturated fatty acid (LCP) status in initially human milk-fed preterm infants from 2 weeks to 6 months postpartum. Twenty-two infants aged 27-33 weeks of gestation at birth who had a birthweight of 710-2525 g were fed human milk for > or = 4 weeks. After discharge from the hospital, they were either human milk-fed or formula-fed according to their mothers' decision: 10 were fully breast-fed for 6 months and 12 were formula-fed after discharge at 1-2 months. The formula fat contained 20% 18:2n-6 and 3% 18:3n-3 but was devoid of long-chain polyunsaturated fatty acids (LCP). Blood samples were taken at 2 weeks, 3 months, and 6 months postpartum. Percentage fatty acid compositions in red blood cell (RBC) and plasma total phospholipids were analyzed by capillary gas liquid chromatography. In formula-fed infants, the change from human milk to formula resulted in a significant rise in plasma and RBC 18:2n-6 and 18:3n-3 and a decrease in plasma 20:4n-6. Interestingly, RBC 20:4n-6 remained constant in both groups, even after 4-5 months of formula feeding. In the formula-fed group, RBC 22:5n-6 showed an increasing trend. The largest changes were seen in 22:6n-3; in the formula-fed group, it decreased in both plasma and RBC, whereas in the human milk-fed group, it showed an increasing trend.(ABSTRACT TRUNCATED AT 250 WORDS)