The anti-allergic drugs disodium cromoglycate (DSCG) and tranilast are strong inhibitors of hyaluronidase. In the development of new anti-allergic drugs, we studied the inhibitory effects of some natural products on the activation of hyaluronidase. Among the compounds tested, liquiritigenin, isoliquiritigenin and baicalein showed dose-related inhibitory effects. Anti-allergic activities of these compounds were evident from the facts that they inhibited the histamine release from rat peritoneal exudate cells induced by antigen, compound 48/80 and calcium ionophore A-23187, and from their inhibitory effect on Shultz-Dale reaction using sensitized guinea pig ileum.