Docosahexaenoic acid [22:6(n -3); 22:6(4,-7,10,13,16,19) (DHA)] is required in quantity by the developing nervous system of the fetus. This need could be met through synthesis of DHA from linolenic acid in the fetus or through placental transfer of DHA directly. To study the placental transfer of n -3 fatty acids, we obtained umbilical and maternal blood samples from 26 healthy women and infants at parturition and measured the fatty acid composition and content of both plasma and erythrocytes. A striking finding was a considerable venous-arterial difference for DHA in the umbilical erythrocytes as a proportion of total fatty acids and