The fatty acid patterns of total serum lipids in the blood of 15 mothers and the mixed cord blood of their newborns were determined by gaschromatography, and the results compared. It is known that the placenta maintains a concentration gradient for lipids between maternal and fetal blood. Quantitative results are given for the total lipid content of the two compartments. The fetal total lipid content was only about one quarter of the mother's. The fatty acid patterns differed characteristically as well, mainly with regard to the concentration of the essential linoleic and arachidonic acid. The linoleic acid level in the maternal blood was high, but low in the mixed blood of the umbilical cord. This was contrasted by low maternal and high fetal levels of arachidonic acid. The placental fatty acid composition was unusual with a 21% content of arachidonic acid. Feeding of a partially-adapted baby food formula resulted in a gradual rise of linoleic acid levels reaching those of adults at the age of 4-9 months.