When a large volume of coagulum remains in the body cavity after trauma or surgery, secondary fibrinolysis occurs, which disturbs the hemostatic balance and results in rebleeding. To better understand this condition, we conducted a clinical study on patients with and without coagula and an experimental study on fibrinolytic activity in a rat model. The results of the clinical study showed that when coagula existed in the body cavity, the blood levels of the fibrin degradation products D-dimer and fibrinopeptide Bbeta15-42 remained high compared with when subjects were under similar stress but without the presence of coagula. In the experimental studies, fibrinolytic activity of the omentum, measured by the fibrin plate method, was higher in rats with hemoperitoneum. This suggests that increased fibrinolytic activity may lead to rebleeding from the area of transient hemostasis when coagulum is present in the body cavity.