This chapter focuses on indolozidine and quinolizidine alkaloids. The alkaloid families falling into this category include Elaeocarpus, Lythraceae, Nuphar, and lupine alkaloids, as well as compounds obtained from amphibians. The bicyclic compound porantherilidine is discussed alongside its tri- and tetracyclic relatives. There are representatives from a cross section of natural sources, including fungi, higher plants, insects, amphibians, and mammals. Two new indolizidine alkaloids have recently been isolated from two species of Solenopsis, a genus of ants in which only pyrrolidine, piperidine, and pyrrolizidine alkaloids detected. The synthesis of indolizidine and quinolizidine alkaloids of Tylophora, Ipomoea, and Elaeocarpus species are also discussed in the chapter. © 1986, Academic Press, Inc.