Amaryllis belladonna bulbs were examined for constituents inhibitory against the murine P-388 lymphocytic leukemia (PS system). Two in vitro active alkaloids, acetylcaranine (2; 9PS ED50 0.23 microgram/ml) and ambelline (3; 9PS ED50 1.6 micrograms/ml), were isolated accompanied by undulatine. However, the non-chiral anhydrolycorinium chloride (5) was found to be the principal antineoplastic (3 PS, 64-69% life extension at dose levels 10 to 20 mg/kg in vivo, ED50 1.4 micrograms/ml in vitro) component. Quaternary chloride 5 has not been located previously among plant or animal biosynthetic products.