During pregnancy, maternal plasma concentrations of the peroxidation-susceptible polyunsaturated fatty acids (polyenes) increase. In addition, the proportion of polyenes is higher in neonatal plasma than in maternal plasma. To study whether these increased amounts of polyenes affect antioxidant levels, we measured lipid-soluble antioxidants in maternal and neonatal plasmas obtained during thirty-five normal pregnancies. These values were then related to the degree of phospholipid-fatty acid unsaturation. Maternal plasma levels of tocopherols and lutein increased during pregnancy, as assessed at 14, 22, and 32 weeks of gestation. However beta-carotene levels decreased, and levels of other carotenoids remained unchanged. Retinol levels were only decreased at 32 weeks of gestation. The value for alpha-tocopherol: phospholipid-polyene unsaturation index (UI) also increased during pregnancy, despite the observed increase in UI. Corresponding ratios for several carotenoids and retinol, however, decreased during pregnancy. After delivery, maternal plasma levels of delta-tocopherol and beta + gamma-tocopherol, as well as beta + gamma-tocopherol: UI values, were lower than values at 32 weeks of gestation. Umbilical-cord plasma antioxidant levels and antioxidant: UI values, except retinol: UI, were significantly lower than maternal values. Significant and consistent cord v. maternal correlations were observed for plasma levels of beta + gamma-tocopherol, lutein and beta-carotene, but not for delta-tocopherol, alpha-tocopherol, lycopene, alpha-carotene, and retinol. In conclusion, although during pregnancy maternal plasma tocopherol levels increased concurrently with, or more than, fatty acid unsaturation in plasma phospholipids, the decrease in carotenoid: UI values during gestation, the decrease in maternal plasma levels of delta-tocopherol and beta + gamma-tocopherol after delivery, and the low neonatal antioxidant levels merit further investigation.