Bioactivity of Quereetin and Its Derivatives     1. Resisting free radicals and anti-oxidation. 10μmol of quercetin is enough to bring about anti-oxidation. Quercetin inhibits lipid peroxidation within the body of hypercholesterolemia-mode hamsters and lowers blood-lipid and cholesterol. Quercetin can markedly inhibit platelet aggregation, selectively combine with the thrombi on the vascular wall,and plays the role of resisting thrombosis by means of inhibiting platelet lipoxidase and epoxidase,so as to enable the endangium to give off thrombolytics and protective mediums of tunica vasculosa.     Quercetin and quercitrin can inhibit the formation of substances like MDA in animal bodies. Since MDA cross linking protein and lipid from the fluorescent substances of senile pigments,it shows that quercetin and its derivatives are effective in resisting senility.     2. Cancer Resisting and Preventing Functions.Research abroad have reported that quercetin is one of the most powerful known anti-carcinogens. It can directly block the proliferation of cancer cells in m-mol concentration. This effect is achieved through inhibiting protein kinase,the enzyme system prerequisite to the growth development of cancer ceils. Quercetin has been proved to be capable of effectively inducing microsomal aryl-hydrocarbon-hydroxylase and epoxide hydrolase so as to cause polycyclic aromatic hydrocarbon and benzopyrene to lose carcinogenic activity through hydroxylation or hydrolysis.     With the fairly systematic and thorough research concerning quercetin and its derivatives both at home and abroad,Fructus Crataegi,a kind of fruit with a fairly high content of quercetin and its derivatives, will,it is expected, further prove to be significant with regard to the treatment and prevention of retrogressive diseases like human anti-cardiopathy,senility and tumors. Its regular pattern of effect is also expected to be brought to light.