78 burned patients (53 males and 25 females) were classified into 4 groups (mild: 14 cases, moderate: 13 cases, severe: 17 cases and extra--severe: 34 cases) in accordance with criteria established by the Chinese Society for Burns. 22 parameters related to platelet, coagulant and anticoagulant factors, fibrinolysis system and hemorheology were determined in the first 24 hours, and on the third and fifth post burn days. The results were as follows: Fibrinogen antigen, von Willebrand factor antigen, plasminogen activator inhibitor activity, thromboxane B2 and hematocrit and whole blood viscosity significantly increased, while antithrombin III, protein C antigen, free protein S and 6-Keto-prostaglandin F1 alpha markedly decreased as compared with normal control in the first 24 hours postburn. In addition, fibrinogen antigen, von Willebrand factor antigen, plasminogen inhibitor activity, thromboxane B2 and whole blood viscosity were persistently elevated, while antithrombin III, protein C, free protein S and 6-Keto-prostaglandin F1 alpha declined on the third and fifth postburn days. These changes resulted in a prethrombotic state, which might be an important factor in the pathogenesis of microthrombosis in burn sites, resulting in deepening of burn wound on the third and fifth days in burn patients.