Chloroform extracts of the root, stem and leaf of Ruta graveolens L. showed significant anti-fertility activity in rats when administered intragastrically on days 1-10 post-coitum. Fractionation of the extracts led to the isolation of chalepensin as the active component with some toxicity. Time-dosing experiments demonstrated that chalepensin acts at the early stages of pregnancy. It is not clear at this stage if the anti-fertility effect is a direct manifestation of chalepensin toxicity.