This chapter presents a comprehensive survey of the occurrence, chemistry, biochemistry, and biological activity of benzophenanthridine alkaloids. There have been a tremendous growth in interest in benzophenanthridine alkaloids, and studies regarding chemistry and biological activity were intensified. Improved methods for the detection and chromatographic separation of quaternary benzophenanthridines were developed, new alkaloids were isolated, and their structures were assigned. There has been an increasing reliance on spectral data-mainly 1H- and 13C-NMR spectra. X-Ray diffraction analyses of (+)-chelidonine, (+)-corynoline, and (+)-lbepicorynoline were reported. Several total syntheses of different types of benzophenanthridines were accomplished. The knowledge of the conformation and chemical reactivity of benzophenanthridine alkaloids helps in better understanding the mode of action and the biosynthesis of these compounds. The benzophenanthridine alkaloids can be classified into six groups on the basis of structures and properties. The group of hexahydrobenzophenanthridine alkaloids is subdivided into chelidonine and corynoline alkaloids, which have an additional 13-methyl group at the B/C ring junction. The largest group is represented with the alkaloids dihydro substituted at C-6. © 1985, Elsevier Science & Technology. All rights reserved.