We investigated the imbalance between thrombin and plasmin activity in vivo with various grades of severity of disseminated intravascular coagulation (DIC) in relation to the underlying diseases. Plasma thrombin-antithrombin-III complex (TAT) and plasmin-alpha 2-antiplasmin complex (PAP) levels were measured in 133 blood samples obtained from patients with DIC. The TAT/PAP ratio was higher in patients with sepsis or solid cancer than in those with hematologic malignancies. In acute promyelocytic leukemia (APL), the TAT levels were the highest, but the PAP levels were even higher and the TAT/PAP ratio was the lowest. As for the severity of DIC, in mild DIC, both thrombin and plasmin activities were increased. In moderate DIC, the TAT/PAP ratio increased, and thrombin activity was much more predominant. However, in severe DIC, the ratio decreased, and plasmin activity became excessive. In 3 patients with acute myeloblastic leukemia, APL and pancreatic cancer, respectively, the PAP level remained high during heparin therapy although the TAT level was decreased. When tranexamic acid was given, the PAP level was selectively reduced, and the TAT/PAP ratio was markedly decreased along with clinical improvement. These results indicate that monitoring of the TAT/PAP ratio may contribute to decisions regarding the institution and performance of combination therapy for DIC using anticoagulants and antifibrinolytic agents.