This chapter presents information on nuphar alkaloids. Nuphar alkaloids were extensively studied in the past decade. Several new C15 and thio-C30 alkaloids were isolated. Special attention was on conformational and configurational problems studied by various chemical and spectral methods. The fragmentation of both C15 and thio-C30 systems was studied by mass spectrometry, and general conclusions were formulated concerning the mechanism of fragmentation and its structural implications. Preliminary biosynthetic studies were carried out using 14C-labeled mevalonic acid. Nupharidine and deoxynupharidine were the most extensively studied C15 alkaloids. The oxidation of deoxynupharidine to nupharidine was found to be almost three times faster than the oxidation of 7-epideoxynupharidine. This was explained in terms of oxidation of deoxynupharidine with inversion on nitrogen to give a cis-fused quinolizidine N-oxide. Nupharolutine is another C15 alkaloid with a hydroxyl group. It was isolated and its structure was established by the Polish–Canadian group of workers. To date, one alkaloid only of the sulfoxide type has been isolated from Nuphar luteum. Because of chemical and spectroscopic evidence, the alkaloid was shown to be neothiobinupharidine sulfoxide that was prepared from neothiobinupharidine by hydrogen peroxide oxidation. Considerable progress has been made in the mass spectrometry of Nuphar alkaloids C15 and C30. © 1977 Academic Press, Inc.