Effects of cyproterone acetate, a steroidal synthetic compound, on the reproductive organs of female gerbils have been investigated. This agent causes reduction of ovarian weights indicative of suppression of pituitary gonadotrophins. Estrogenic nature of cyproterone acetate was investigated in intact and ovariectomized gerbils taking uterine weight, vaginal keratinization and glycogen contents are parameters of estrogenic action. Cyproterone acetate in ovariectomized gerbils induced vaginal keratinization, increase in uterine weight, protein, RNA, glycogen and sialic acid contents of uterus, thus indicating an estrogenic activity. The histological and biochemical parameters lead to the conclusion that cyproterone acetate possesses estrogenic properties.