A high uterine glycogen occurs in the rat during proestrus and estrus, and lower values at metestrus and diestrus. Estrogens increased the uterine glycogen of adult and immature rats (estradiol monobenzoate, estrone and dioxydiethylstilbestrol). 24 and 48 hr. fasts did not change uterine glycogen. The estrogens increased uterine glycogen in adrenalectomized rats. Epinephrine did not reduce uterine glycogen. Progesterone did not increase the effect of estrogen. Most of the glycogen was in the myometrium; no change of endometrial glycogen occurred during hormonal treatment. Estrogens failed to alter skeletal muscle glycogen.