Studies of the effects of megestrol (6-methyl, 6-dehydro, 17alpha-acetoxy progesterone) on human subjects indicated that this drug is a potent, orally effective progestational agent. The progestational effect was enhanced by estrogen. When combined with ethinyl estradiol satisfactory control of menstrual function and inhibition of ovulation were achieved. Increasing doses of this combination were effective in four patients with endometriosis. Side effects of the drug were minimal. No toxic effects on adrenal, hepatic or hematopoietic function were noted.