This study was carried out to compare plasma lipid pattern in breastfed and formula-fed infants and the effects of exchanging breast milk for formula and of introducing weaning foods. Healthy infants, exclusively breastfed at least until 3 mo, were at this age randomly assigned to infant formulas with similar fat composition. Formula was gradually introduced when breastfeeding was discontinued. One group continued to breastfeed beyond 6 mo of age. All infants received the same weaning foods and were studied between 3 and 12 mo of age. Decreased plasma concentrations of total and low-density lipoprotein cholesterol (TC, LDL-C), apolipoprotein B (apo B) and A1 (p < 0.001), and of high-density lipoprotein cholesterol (p < 0.05) were found when breast milk was exchanged for formula before 6 mo. At this age plasma TC, LDL-C and apo B were lower in formula-fed than in breastfed infants (p < 0.001). These plasma lipids then increased (p < 0.01) when the intake of formula decreased and that of weaning foods increased. However, plasma TC and/or LDL-C remained lower at 12 mo in formula-fed than in breastfed infants (p < 0.05). Our results indicate that the plasma lipid profile of infants is highly responsive to the dietary nutrient intake, as indicated by the decrease in plasma lipids and apolipoproteins when breast milk was exchanged for formula and by the increase in these concentrations when the intake of weaning foods gradually increased.