The two antiestrogens studied, viz. norethindrone (10, 25, 50 μg/rat daily for 10 days, sc) and depoprovera (1, 5, 10 μg/rat daily for 10 days, sc) delay ovulation when given during estrogen dominated phase of the cycle. Norethindrone and depoprovera reduce the glycogen content as well as the activities of total and active phosphorylase of rat uterus in a dose-dependent manner. Discontinuation of treatment normalises the changes. Of these two antiestrogens, depoprovera is at least 5-times more potent.