Abstract: The total alkaloids of Sinomenium acutum, fed by stomach tube or injected intravenously, produced a definite hypotensive effect in both anaesthetized and unanaesthetized animals. The onset was fast; the hypotension was marked and lasted 2—4 hours. Tachyphylaxis developed on repeated medications. This hypotension was mediated via the adrenolytic action and the nervous reflex mechanism, but not the histamine liberation. The alkaloids did not block ganglions, and exerted no influence on the M-cholinergic reactive system. Direct vasodilation was not observed. In anaesthetized dogs, intravenous injections of the alkaloids 1—2 mg/kg decreased the cardiac output, yet not the total peripheral resistance. Three renal hypertensive dogs were fed 10—40mg/kg/day for 15 days. The hypotensive effect was insignificant, owing probably to tachyphylaxis. The EKG, serum BSP retention, and blood NPN level revealed nothing abnormal. One of the three dogs collapsed immediately after the first medication, but tolerated well after the succeeding doses. Two normal dogs were fed 20—160 mg/kg/day for 16 days. Untoward reactions were not noticed, except a slight elevation of blood NPN in 1 dog.