The alkaloids lycorine, 1-O-acetyllycorine and ismine were isolated from the basic dichloromethane-soluble fraction of Crinum x powellii "Albu m" bulbs. The alkaloid structures were established by physical and spectroscopic analyses, including 1D NMR techniques and GC-MS analysis. The three alkaloids are reported for the first time for this hybrid. Additionally, the three alkaloids isolated were tested against a mechanism-based bioassay utilizing genetically engineered mutants of the yeast Saccharomyces cerevisiae strains RAD+, RAD52Y and RS321 where lycorine was the only alkaloid that displayed moderate topoisomerase I inhibitory activity.