Silvestrol((-)-Silvestrol) is the novel cyclopenta[b]benzofuran, silvestrol, isolated from the fruits and twigs of Aglaia foveolata. Silvestrol((-)-Silvestrol) has been found to exhibit very potent in vitro cytotoxic activity against several human cancer cell lines. Furthermore,Silvestrol((-)-Silvestrol) was active in the in vivo P388 murine leukemia model.