[Ovulation inhibition with RU 486]

Starting from the theory, that progesterone (P) may be one of the triggers of physiologic ovulation, P receptor blocking agent Mifepristone was administered to 7 regularly menstruating women, 2 days before the expected time of ovulation. Ovulation was monitored by ultrasound folliculometry and determination of serum estradiol (E2), P and luteinizing hormone (LH) levels. The luteal phase was checked by measuring urinary pregnandiol glucuronide excretion. Administration of the drug was properly timed in 5 cases, none of the existing follicles ruptured, one got luteinized and 4 had undergone atresia. According to these findings P seems to be a trigger of ovulatory events.