The pathogenesis of chronic subdural hematoma is not fully understood. It is thought that fibrinolytic hyperactivity within the hematoma capsule plays an important role. However, since this hyperactivity has not been found in the systemic blood, accelerated fibrinolysis is thought to occur only locally. To evaluate coagulant and fibrinolytic activities in the peripheral blood, the authors measured fibrinopeptide A (FPA) and fibrinopeptide B beta 15-42 (FPB beta), which are relatively sensitive hematologic factors, in 14 patients with chronic subdural hematoma. Peripheral venous blood was collected within 24 hours before surgery and FPA and FPB beta levels were determined. In the eight cases followed for more than 1 month after surgery, pre- and postoperative FPA and FPB beta values were compared. The possible relationship between preoperative FPB beta and hematoma density as well as elevated intracranial pressure (judged by preoperative computed tomography) was also examined. The following results were obtained: 1) Preoperative FPA and FPB beta values were both statistically significantly elevated suggesting systemic acceleration of coagulant and fibrinolytic activities. FPB beta levels exceeded those of FPA in almost all cases, indicating that fibrinolysis was more dramatically enhanced. 2) Many patients with high FPB beta values had high-density areas on computed tomography scans. 3) Patients with choked disc had high FPB beta values, suggesting a correlation between chronic intracranial hypertension and FPB beta. 4) Postoperatively, there was a marked decrease in FPA values, whereas FPB beta values remained above normal, which may reflect persistence of accelerated systemic fibrinolytic activity in patients with chronic subdural hematoma.