Besides inhibition of cornification of vaginal epithelium Org30958 (ORG 30958) decreases ovarian aromatase and plasma E2 levels in DHEAS-treated hypophysectomized rats. Plasma estradiol levels are also lowered by Org30958 in dogs which are treated with pregnant mare serum gonadotrophin in order to induce pro-estrus. Org30958 displays much less than 1/400th of the androgenic activity of testosterone propionate in immature castrated rats and appears to be devoid of estrogenic and anti-estrogenic activity in ovariectomized mature rats. A twice daily dose of 1.5 mg Org30958/kg postpones ovulation in mature female rats^[1].