Aortic thrombosis in de-endotheliazed rabbit and 51Cr labeled autologous platelets were used for the evaluation of in vivo effects of CsB-851 on platelet-vessel wall interaction. The result showed that when CsB-851, an active part of alcoholic extract of mycelium from Cordyceps sinensis (Berk.) Sacc., was infused intravenously, the 51Cr labeled platelet number per gram dry weight of injured abdominal aorta (98.14 +/- 9.41 x 10(6)) was much lower than that in the control group (201.25 +/- 27.21 x 10(6)) in a concentration dependent manner. This indicated that CsB-851 could inhibit thrombus formation at the de-endotheliazed surface of the aorta. Since it could inhibit platelet aggregation in vitro had no effect on coagulation function in vivo, it seemed that the inhibitory effect of CsB-851 on arterial thrombus formation was mainly related to the inhibition of platelet functions.