A series of 70 labile 17-ethers of estradiol has been synthesized and tested for uterotrophic activity. Most of the compounds proved to be more active orally than estradiol and some of them comparable with ethinylestradiol. Particularly high oral activity was displayed by enol ethers of 3-pentanone and of fiveto nine-membered cyclanones and by mixed ketals. The cycloalkenyl ethers, mainly those deriving from 8-1 5-membered cyclanones, displayed ...