17alpha-ethynylestradiol is a 3-hydroxy steroid that is estradiol substituted by a ethynyl group at position 17. It is a xenoestrogen synthesized from estradiol and has been shown to exhibit high estrogenic potency on oral administration. It has a role as a xenoestrogen. It is a 17-hydroxy steroid, a terminal acetylenic compound and a 3-hydroxy steroid. It is functionally related to a 17beta-estradiol and an estradiol.