Extracts of Erythrina addisoniae are frequently used in the traditional medicine of Western Africa, but only insufficient information about active compounds is available. From the stem bark of Erythrina addisoniae, three new (1, 2, 4) and three known (3, 5, 6) flavanones were isolated: addisoniaflavanones I and II, containing either a 2´´,3´´-epoxyprenyl moiety (1) or a 2´´,3´´-dihydroxyprenyl moiety (2) were shown to be highly toxic (MTT-assay: EC 50 -values of 5.25 +/-13.5 and 8.5 +/-15.2 µM, respectively) against H4IIE hepatoma cells. The cytotoxic potential of the other isolated flavanones was weaker (range of EC 50 -values between 15 and >100 µM). Toxic effects of addisoniaflavanone I and II were detectable after 3 h (MTT assay). Both compounds induced an apoptotic cell death (caspase 3/7 activation, nuclear fragmentation) in the hepatoma cells and, at high concentrations, also necrosis (membrane disruption: ethidium bromide staining), Formation of DNA strand breaks was not detectable after incubation with these compounds (comet assay). In conclusion, the new prenylated flavanones addisoniaflavanones I and II may be of interest for pharmacological purposes (e.g. potential use as cytostatic drugs) due to their high cytotoxic and pro-apoptotic potential.