Plasma ethinylestradiol increases 47.6% when taken with ascorbic acid because of competition in producing sulfate conjugation. Thus the role of sulfates may be important. Serum and urinary estrone sulfate (E1-S) in pregnancy and non-pregnancy were analyzed. Its serum peak during the menstrual cycle was 2.67 +/- 0.37 ng/ml (mean +/- SE) and about ten times that of estradiol-17 beta. E1-S showed lower levels in malignant tissues of breast cancer and endometrial cancer. Increased sulfatase activity in the malignant tissue hydrolyzes E1-S to E1, which may develop the tumors. Serum estradiol 17-sulfate (E2-17-S) in pregnancy was first measured. As E2-17-S decreased, lipid peroxides increased. E2-17-S is converted to 2-OH or 4-OH E2-17-S, which act as lipid peroxide scavengers. Pregnancy-induced hypertension showed lower levels of E2-17-S. In vitro study using the human endothelial cell of the aorta, E2-17-S and 2-OH E2-17-S strongly suppressed lipid peroxidation, which precedes atherosclerotic change.