From fresh, mature seeds of Zephyranthes flava, two new 2-oxyphenanthridinium alkaloids, zefbetaine and zeflabetaine along with 15 known free and glucosyloxy alkaloids have been isolated by gradient solvent extraction, chromatography and derivatization. The new compounds have been characterized by comprehensive spectroscopic analyses, chemical transformations and synthesis. Additionally, changes in the major alkaloids during development of the fruits have been analysed and their biological significance appraised. © 1986.