Increase of TAT is reflected by the generation of thrombin in hypercoagulable state. TAT might increase in DIC characterized by the formation of disseminated micro-thrombosis. DIC was classified into three groups according to the results of screening tests (FDP, platelet count, fibrinogen, prothrombin time). TAT values significantly increased in the stage of pre-DIC compared with the control group consisting of DIC prone underlying disease. Pre-DIC was easily detected by an increase of TAT during the clinical course. Management of high TAT began with the use of an anticoagulant such as heparin under the condition of sufficient ATIII level. The lowering effect of TAT was easily obtained by the anticoagulant. In ATIII-deficient DIC, the high TAT reduced with the substitution of ATIII concentrate, though a transient increase of TAT was found during the administration of ATIII. To reduce the high TAT under the deficient state of ATIII, MD805, a synthetic thrombin inhibitor, was introduced to avoid further consumption of ATIII. The TAT was decreased by the use of MD805 without administration of ATIII. MD805 could be used as an effective anticoagulant in high TAT due to DIC under an ATIII-deficient state. Although the TAT improved with an adequate anticoagulation in DIC, spontaneous bleeding sometimes appeared as a complication associated with the high level of alpha 2 plasmin inhibitor plasmin complex. In this case, the combined use of tranexamic acid relieved the bleeding.