The initial isolation of a specific alkaloid from the genus Crotalaria is reported. This compound has been named monocrotaline and was isolated from C. spectabilis Roth. The compound melts at 196-197°, and has been given the empirical formula C16H26O6N, tentatively. The identity of the compound as the toxic principle of C. spectabilis has been established. © 1935, American Chemical Society. All rights reserved.