The short-term toxicity of sanguinarine, a benzophenanthridine alkaloid, and of two alkaloid extracts of Sanguinaria canadensis L. are presented. The acute oral LD50 in rats of sanguinarine was calculated to be 1658 mg/kg, and of the two alkaloid extracts, 1440 and 1250 mg/kg. The acute iv LD50 in rats of sanguinarine was found to be 29 mg/kg. No toxic effects were observed in rats fed up to 150 ppm sanguinarine in the diet for 14 d and in rats treated by gavage with up to 0.6 mg/kg body weight for 30 d. The acute dermal LD50 in rabbits was found to be greater than 200 mg/kg.