Abstract: The "Compound Mixture of Two Fairies" has been used clinically for treatment of hypertension. It is composed of Curculigo ensifolio, Epimedium, sp., Morinda officinalis, Phellodendron chinense, Anemarrhena asphodeloides, and Angelica sinensis. In normal dogs, intragastric administrations of 6g (crude drugs) per kg t.i.d, for 20 days produced no toxic reactions: If the dosage was increased 3—4 times, emesis and diarrhea occurred, probably due to alimentary disorder from the bulk of the decoction. When the Compound Mixture was introduced 6. g/kg into the lumen of duodenum in anesthetized cats, the blood pressure began to descend at 30 minutes, and lowered an average of 30% below the original level in 2 hours. Four Goldblatt renal hypertensive dogs were given the Compound Mixture by stomach tube. The dose for the first 10 days Was 9 g/kg/day, and doubled for the next, 10 days. The post-medication observation period was another 10 days. Blood pressure was measured daily by auscultation on the carotid loop. The average reduction of the diastolic pressure in the space of 30 days was 10 mm Hg (8%), and that for the lowest 5 days running was 16 mm Hg (12%). A therapeutic action (a reduction of at least 11 mm Hg diastolic) was demonstrated in 3 dogs. Among them 2 dogs received a second course of treatment which appeared to be equally efficacious. Intraperitoneal injections of the Compound Mixture 6 g/kg to anesthetized dogs resulted in a decrease of cardiac output during the hypotension, while the dilatation of peripheral vessels was insignificant. Comparative experiments on the 6 ingredients revealed that the hypotensive action of "Compound Mixture of Two Fairies" could be primarily attributed to Phellodendron chinense and Epimedium sp., whereas Curculigo ensifolio alone had little effect. Eight hypertensive dogs were fed daily the Compound Mixture or a mixture of 6 decoctions of the components. Analysis of variance disclosed that the hypotensive potency of the former was no better than the latter. Hypertensive dogs were fed the Compound Mixture which was devoid of Morinda officinalis, and the therapeutic potency was shown to be no less than that of "Compound Mixture of Two Fairies". Hence, we deem that Morinda officinalis is dispensable.