It is widely accepted that atherosclerosis and thrombus formation are closely associated. Recent progress in the development of molecular markers of blood coagulation and platelet enabled us to estimate even the slight activation of blood coagulation and platelet activation systems. We investigated a contract phase-activate coagulation and factor -inhibitor complex (factor XIa-alpha 1 antitrypsin) and expression of CD62P on platelet surface, a specific antigen on platelet, in patients with coronary arterial diseases. We compared these activation markers after stratifying patients according to the number of significant coronary artery stenoses. Patients with three-vessel disease had significantly increased levels of factor XIa-alpha 1 antitrypsin, fibrinogen, and CD62P expression compared to those in other subgroups. Although it is unknown whether these abnormalities are the cause or the result of the vascular lesion, these findings may be important to understand the pathophysiology underlying atherosclerosis or propagation of the atherosclerotic process itself.