The presence of a 17beta-hydroxyl group endows the simple androstane molecule with the ability to produce growth of the uterus, vagina, and prostate of the female hypophysectomized albino rat. It appears that hydrogen atoms at position 17 are of critical importance since related compounds with a ketone group at this site are inactive. Monofunctional steroids with a hydroxyl or a ketone group at position 3 likewise are devoid of activity. If a phenolic A-ring is present in monofunctional steroids the 17beta-hydroxyl group is not obligatory for growth. Proliferation of the uterus and vagina were found to follow the administration of 17-desoxyestradiol.