Recent statements concerning linoleic (LA) and alpha-linolenic acid (LNA) intakes for infants include a desirable range of LA/LNA ratios. To evaluate several dietary LA/LNA ratios, the fatty acid patterns of plasma and erythrocyte phospholipid fractions, as well as plasma total lipid fractions, were determined shortly after birth and at 21, 60, and 120 d of age in term infants fed formula with 16% of fat as LA and either 0.4, 0.95, 1.7, or 3.2% as LNA (LA/LNA ratios of approximately 44, 18, 10, and 5). The content of all n-3 fatty acids in both plasma fractions was higher at all times in infants who received the highest LNA intake; however, the docosahexaenoic acid (DHA) content was only half that shortly after birth or reported in breast-fed infants of comparable ages. The LA content of plasma lipids of all groups was higher at all times than shortly after birth but did not differ among groups. The arachidonic acid (AA) content was higher in infants who received the lowest LNA intake, but only half that at birth or reported in breast-fed infants. In contrast, the DHA content of the erythrocyte phospholipid fraction did not differ among groups until 120 d of age when it was higher in those who received the highest LNA intake and the AA content of this fraction did not differ among groups at any time. These data demonstrate that dietary LA/LNA ratios between 5 and 44 do not result in plasma or erythrocyte lipid levels of DHA or plasma lipid levels of AA similar to those at birth or reported by others in breast-fed infants. However, the data indicate that the LA/LNA ratio of the formula is an important determinant of the amounts of DHA and AA required to achieve plasma and erythrocyte levels of these fatty acids similar to those of breast-fed infants.