Objectives: It is well known that malignant diseases exhibit an increased propensity to clotting and fibrinolytic aberrations and early detection of these hemostatic alterations is very important for the rapid institution of appropriate treatment of thromboembolic and hemorrhagic complications in patients with malignant disease. The incidence of these abnormalities in lung cancer was reported from 20% up to 95% according to various investigators using different hemostatic parameters. We measured the concentrations of plasma thrombin-antithrombin III complex(TAT) and plasmin-a2-plasmin inhibitor complex(PIC), which are newly developed sensitive molecular markers of coagulation and fibrinolysis system respectively in patients with lung cancer and determined the degree of these hemostatic abnormalities according to the histologic types and different clinical stages in patients with lung cancer. Methods: We measured the concentrations of plasma TAT and PIC in 62 patients with histologically corned lung cancer, and we determined stage radiologically in non-surgical patients and pathologically in surgical patients. The plasma TAT and PIC levels were assayed using a solid phase enzyme immunoassay with Enzygnost-TAT kit(Behringwerke, Marburg, Germany) and Enzygnost-PAP kit(Behringwerke, Marburg, Germany), respectively. Results ' The concentrations of plasma TAT(6.8±4.8 ng/mL) and PIC(644.3±330.5 ng/mL) in patients with lung cancer were significantly increased compared to those of plasma TAT(2.8±1.2 ng/mL) and PIC(240.4±69.7 ng/mL) in control subjects(p<0.05), The concentrations of plasma TAT and PIC in patients with lung cancer were not different according to histologic types, clinical stage and distant metastasis. There was no correlations between TAT and PIC(r=0.11, p > 0.05). Conclusions: There was a subclinical activation of coagulation and fibrinolysis system in patients with lung cancer although they don't have overt clinical evidences of thromboembolism or hemorrhage. Rut there were no different activation of coagulation and fibrinolysis system according to histologic types and clinical stages.