Significantly higher (P < 0.05) thrombin-antithrombin III complex levels were found in the abdominal exudate of patients with peritonitis (median 5500 ng/ml) than in that of controls (median 89 ng/ml). In patients, peritoneal fluid concentrations of tissue and urokinase-type plasminogen activator were increased by factors of 65 and 10 respectively (P < 0.05). The concentration of plasminogen activator inhibitor (PAI) 1 was increased by a factor of about 800 (median 395 versus 0.5 ng/ml, P < 0.05). Despite markedly raised concentrations of PAI, peritoneal fluid displayed fibrinolytic activity as demonstrated by significantly increased (P < 0.05) concentrations of plasmin-α2-antiplasmin complex (median 10 952 versus 57 ng/ml) and fibrin degradation products (median 40 360 versus 126 ng/ml). There was no correlation between plasma and peritoneal fluid concentrations. Intra-abdominal coagulation and fibrinolysis are stimulated in the abdominal cavity of patients with bacterial peritonitis.