The occurrence of a new type of bufotoxin, in which L-glutamine replaces the arginine residue of hitherto known "bufotoxin," in the skin of the North American toad, Bufo americanus, is reported. Two novel bufotoxins, 3-suberoyl-L-glutamine esters of marinobufagin and telocinobufagin, were separated by column chromatography on silica gel, high-performance liquid chromatography and gel chromatography on Sephadex LH-20, and their structures were elucidated by degradative and synthetic studies.