A new naturally occurring isoflavone, derrone, was isolated from Ulex jussiaei (Leguminosae) together with the isoflavones ulexins A-C, lupalbigenin, isolupalbigenin, 7-O-methylso-lupalbigenin, isoderrone, ulexone A and isochandalone, the pterocarpans (6aR,11aR)-(-)-maackiain, (6aR,11aR)-(-)-2-methoxymaackiain and (6aR,11aR)-(-)-4-methoxymaackiain, the chalcone 4-hydroxylonchocarpine and the dihydrochalcone crotaramosmine. The antifungal activity of the new compound was tested by a bioautographic method against Cladosporium cucumerinum, and as expected from structural features it proved to have no activity.