The furanopterocarpan, neodunol, has been isolated as a major phytoalexin from the fungus-inoculated stems of Pachyrrhizus erosus. Neodunol is accompanied by small quantities of demethylmedicarpin and a third compound provisionally identified as the prenylated pterocarpan, homoedudiol; traces of a neodunol isomer were also isolated from P. erosus although its precise structure could not be determined. The apparently close chemical relationship between Pachyrrhizus and Neorautanenia is discussed in the light of a recent study which allocates these genera to different sections of the legume tribe Phaseoleae.