The steroid RU-486 (mifepristone) is an antiprogesterone that works at the receptor level. It can interrupt pregnancy very early on (contragestion), mostly by interfering with the process of implantation and decidua function. It also may facilitate surgical evacuation of the uterus and certain difficult deliveries. It impedes ovulation when taken during the follicular phase. Also, RU-486 is the first antiglucocorticosteroid available for clinical use. It deserves further studies to assess its wide range of therapeutic potential.