Evidence is presented to show that the seeds of species of Erythrina contain another alkaloidal fraction besides what has been designated as the free (classical) alkaloidal fraction. This new fraction, designated the combined alkaloidal fraction, has been shown to yield on acid (preferably) or alkaline hydrolysis, a liberated alkaloidal fraction. From these liberated alkaloidal fractions of eight species of Erythrina, four new liberated Erythrina alkaloids were isolated and characterized. A system of nomenclature for the Erythrina alkaloids has been adopted, and the four new ones herein described from the liberated fractions have been named erysodine (C18H21NO3), erysopine (C17H19NO3), erysocine (C18H21NO3), and erysovine (C18H21NO3). These four new alkaloids are all active for curare-like action on frogs. Certain preliminary facts on the functional groups and structures of these four alkaloids have been described, and additional data will be presented in future papers. © 1940, American Chemical Society. All rights reserved.