Various extracts of Ferula jaeschkeana Vatke have been studied for their anti-implantation activity in rats and hamsters along with an assessment of hormonal properties like estrogenic, antiestrogenic, progestagenic and antiprogestagenic actions. Of the various extracts produced, hexane, benzene and chloroform fractions prevented implantation in all the rats when administered at 25 mg/kg dose for 7 days after coitus. These fractions were ineffective in golden hamsters. In the hormonal studies, the hexane extract increased significantly the uterine wet weight in bilaterally ovariectomized rats and also stimulated the histological features of the uterus. Its estrogenic activity has also been confirmed by its capacity to induce implantation in rats undergoing experimentally delayed implantation. Its conjoint administration with diethylstilbesterol showed a synergistic effect. None of the doses of the hexane extract could interfere with the action of standard progesterone when tested in mature and immature rats. The anti-implantation activity of the extracts was considered to be due to its frank and potent estrogenic action.