A partially purified follicle-stimulating hormone preparation (human pituitary FSH) has been obtained from human pituitaries. The ovarian response to this preparation was studied in 7 amenorrheic women. The effect of human chorionic gonadotropin (HCG) was studied in addition. In 4 patients exhibiting no endometrial activity or only slight proliferation, HCG alone did not induce ovulation and had no effect on the size of the uterus, on the endometrium, or on the urinary excretion of estrogen and pregnanediol. In 2 patients showing endometrial proliferation, the administration of HCG alone was followed by ovulation, a secretory transformation of the endometrium, and a marked increase in urinary pregnanediol excretion. The administration of human pituitary FSH alone to 2 patients resulted in an increase in the size of the uterine cavity, in polycystic enlargement of the ovaries, and in a pronounced increase in urinary estrogen output. Treatment with human pituitary FSH followed by HCG produced in all patients polycystic enlargement of the ovaries, ovulation in 4 out of 5, and a secretory transformation of the endometrium in 3 out of these 5 patients. Ovulation was accompanied by a marked increase in the urinary excretion of both estrogen and pregnanediol.