Hydrastis canadensis L (Ranunculaceae) is a small perennial herb native of North America, whose rhizome and root are widely utilized for their vasoconstrictor and haemostatic activities (1 —3). In a previous study on the hypogeon parts of H.canadensis, together with the main alkaloids berberine, /3 hydrastine, canadine, and canadaline, one of us reported the isolation and the identification of five other benzylisoquinoline alkaloids (4). In addition, a tenth alkaloid was isolated, but its structure remained undetermined. This paper reports the chemical characterization of this additional alkaloid, for which we propose the name of canadinic acid (1).