The biochemical effect of vitamin E supplementation to mothers with threatened premature delivery and to premature infants after birth has been studied. Although a weak correlation was found between maternal and cord blood vitamin E levels at birth, cord blood levels were not significantly higher in the infants from supplemented mothers than those from unsupplemented mothers. Furthermore, maternal vitamin E treatment did not prevent either erythrocyte hemolysis or lipid peroxide formation in the premature infants after birth. On the other hand, intramuscular vitamin E to infants after birth produced a marked biochemical effect, with both zero erythrocyte hemolysis and low lipid peroxide formation when serum vitamin E increased above 2 mg/100 ml. We conclude that intramuscular vitamin E immediately after birth is necessary to achieve a biochemical effect of vitamin E in the early neonatal period. (No cases of retrolental fibroplasia occurred in the present study.)