Abstract: The root of Jin Qiao Mai (Fagopyrum cymosum (Trey.) Meisn.), a species of Po-lygonaceae, has been used for the treatment of pulmonary sepsis. Flavanol (5, 7, 3',4'-tetrahydroxyflan-3-01 dipolymers) was demonstrated to be its chief effective compo-nent. Both the extract of Jin Qiao Mai and flavanol exhibited no significant antibac-terial action in vitro. No antibacterial substance was found in the urine of either mice or men nor was it found in the organs of mice given the extract p. o.Therapeutic effect was shown in mice infected i. p. with Staphylococcus aureus only when the extract or flavanol was given via the same route. Phagocytic action of peri-toneal macrophages was enhanced, but the number of macrophages was not increased when the extract or flavanol was given i. p. to mice. Antipyretic action was demonstrated in rabbits. Flavanol was shown to be anti-inflammatory in mice and rats. Platelet aggregation in rats induced by ADP and Staphylococcus aureus in vitro was inhibited by flavanol. The same effect on platelet aggregation induced by ADP and collagen was found when flavanol was given i. v. to rats. Flavanol given i. v. showed also expe-ctorant effect in mice as shown by the phenol red method, but the bronchial excretion was not increased.The method for elucidating the mechanism of action of traditional medical herbs with therapeutic effect in treating infective diseases is discussed, based on the pathophy-siological changes of infective diseases.