A new alkaloid designated as erythroculine was isolated from the leaves of Cocculus laurifolius DC. (Menispermaceae). From degradative and spectroscopic studies, the structure (I) was assigned to this alkaloid and this assignment was then definitely confirmed by chemical correlation of erythroculine with tetrahydroerysotrine (XXII) of established stereochemistry. From the view point of biosynthesis of erythrina alkaloid, a carbomethoxyl group on a benzene ring is unusual and the isolation of this alkaloid makes the third example of erythrina alkaloid in Cocculus species. © 1970, The Pharmaceutical Society of Japan. All rights reserved.