This chapter presents information on hasubanan alkaloids. The chapter discusses the significant advances of the hasubanan group in discovering thirteen new congeners post-1970, including synthetic studies of the hasubanan skeleton. The occurrence of the hasubanan alkaloids has been noted in Stephania species only. The numbering system of the hasubanan skeleton (2,3,4,5- tetrahydro-3a,9b-butano-1H- benz[e]indole) is used throughout this review. The chapter presents a table that presents a survey of the occurrence and physical constants of hasubanan alkaloids. The mass spectral feature exhibits a very characteristic fragmentation pattern and, therefore, provides a rapid and convenient method for structure elucidation of hasubanan alkaloids, especially, that of alkaloids obtained in small amounts. Alkaloids, such as hasubanonine, possessing a , β-unsaturated carbonyl group at C ring, show a similar breakdown pathway as that of metaphanine and others. Stephisoferuline was isolated from Stephania hernandifolia, and the presence of four methoxyl groups, one secondary amino group, a , β-unsaturated ester moiety, and two phenolic hydroxyl groups was shown. Hasubanonine and protostephanine have been shown by tracer experiments to be biosynthesized from two different C-6–C-2 units. Four 14C-labeled amines and the putative isoquinoline intermediates were synthesized and tested in Stephania japonica plants. © 1977 Academic Press, Inc.