The administration of partially purified homologous follicular stimulating hormone to adult females ofRana esculentahypophysectomized during the growth phase of the ovaries is followed by an increase of estrogens and progesterone in the blood. The luteinizing hormone seems to act by increasing only the progesterone level. These effects are eliminated by ovariectomy. In autumn and winter, hypophysectomy seems to affect only slightly the low levels of circulating hormones, probably because in that period the gonads are less sensitive to hormones from the pituitary.