Abstract: Dauricine (Dau), an isoquinoline alkaloid extracted from the roots of Menispermum dauricum D. C. and used as an antiarrhythmic agent in China recently, was shown to inhibit rat platelet aggregation induced by arachidonic acid (AA) and ADP, as well as human platelet aggregation induced by AA, ADP and adrenaline(Adr) in vitro in a dose-dependent manner The concentration of Dau required for 50% inhibition (IC₅₀) of rat platelet aggregation induced by AA and ADP was 26 and 37 μmol/L, respectively. For human platelet aggregation induced by AA, ADP and Adr the IC₅₀ of Dau was found to be 39,55 and 43 μmol/L, respectively. Dau inhibited the cyclooxygenase pathway metabolites of AA (TXB₂ and HHT) in washed intact rat platelets. The production of TXB₂ and HHT was reduced by 26% and 19%,respectively, when the Dau concentration was 50 μmol/L and by 46 and 45%, respectively, when the concentration of Dau was 100 μmol/L. The formation of 12-HETE was also inhibited at 100μmol/L of Dau. The inhibitory effect of Dau on AA metabolism may be one of the machanisms related to. its inhibition of platelet aggregation.