17 beta-Acetoxy-5 alpha, 17 alpha-pregn-2-ene-20-yne (TX 380) strongly suppresses the hypophyso-gonadic axis at central and peripheral levels. Depending on the dosage and on the hormonal status at the time of treatment, this combined inhibition results in major disturbances of the estrus cycle and in impaired ovulation. TX 380 shows minimal androgenic activity. It exerts no effect on the fetal female urogenital tract during gestation. TX 380 possesses only weak estrogenic properties, and does not promote endometrial proliferation in the female rabbit. Moreover, it markedly opposes the action of progesterone. Given this pharmacological profile, TX 380 stands as a candidate drug in the treatment of gynecologic affections, such as endometriosis and benign breast disease, and as a potential contraceptive agent.