The alkaloid of Banisteria Caapi is harmine, proved directly with the harmine of Peganum harmala, by analyses, preparation of derivatives, absorption spectra, toxicity in mice, and symptomatology in monkeys. The previously proposed names of telepathine, yajeine, and banisterine, for the same alkaloid should, therefore, be dismissed. In mice and rabbits a limited detoxification of harmine by sodium amytal has been demonstrated.