Abstract: Magnoflorine (Mf) a quaternary ammonium base, has been isolated from the Chinese herb Tu Qing Mu Xiang (roots of Aristolochia debilis Sieb. et Zucc.) as its hypotensive principle. The results of our pharmacological studies on this alkaloid are reported as follows: 1. In anesthetized cats intravenous injection of Mf (2mg/kg) produced a prompt and significant fall of the blood pressure, lasting about 1-2 hours. Oral administration (20, 40mg/kg) also resulted in hypotension (Fig. 1). 2. In unanesthetized rats and in a Goldblatt hypertensive dog, Mf injected either intraperitoneally or intravenously, also exhibited a hypotensive action (Fig. 2, 3). 3. Mf gave no noticeable effect on the M-cholinergic reactive system. It inhibited the N-cholinergic reactive system: its ganglionic blocking action being about half as active as that of hexamethonium (c₆) (Fig. 6). Some curarelike action was also noticed (Fig. 8). On the adrenergic reactive system it showed practically no effect. The hypotensive action of Mf is, therefore, mainly associated with its ganglionic blockade. 4. The acute LD₅₀ of Mf by intravenous injection in mice was 0.02 g/kg. Oral medication with a 10-fold dose daily for 4 weeks neither elicited any toxic symptoms nor retarded the growth.