Term infants have precise dietary fat requirements for their metabolic, energy and structural needs. The fat content of commercial milk formulae differs from maternal milk in that it contains no long-chain polyunsaturated derivatives or cholesterol. Artificially fed children thus have less of these molecules available for their biological needs, and hence lower levels of long-chain polyunsaturated derivatives in circulating and membrane lipids than breast-fed children. The functional effects of this difference have not been investigated thoroughly in term infants. Dietary lack of essential fatty acids and their derivatives is evident also in weaned children during the second half of their first year of life. Qualitative changes in the fat content of commercial milk formulae could help to correct some widely encountered dietary imbalances, using the pattern of fats provided in breast milk as the ideal.