PIP: 37 women, 18-45 years old, were administered diethylstilbestrol (DES), 20 mg 3 times daily over the course of 5 days 24-48 hours after unprotected intercourse during the estimated time of ovulation. Pregnancy was registered in only 1 case. The effects of DES on the levels of follicle stimulating hormone, luteinizing hormone (LH), and progesterone were determined in 7 of these women during the entire course of a cycle. A decrease in the level of LH was the only abberation found in comparison with a normal control group. Ovulation was not suppressed by the application of DES. Progesterone values in the luteal phase were normal for 4 women, while 3 showed a more rapid decrease in this level, which preceded menstruation by 3-5 days. It was observed that after the administration of DES luteolysis did not occur in the ovulatory phase, although the ovulatory mechanism was disrupted.