Summary Fibrinolytic activity and inhibitory activity was measured in 36 malignant ascites and 20 cirrhotic ascites using euglobulin fibrinolytic activity, fibrin autography, reverse fibrin autography and quantitation of tissue-type plasminogen activator (t-PA), urokinase-type plasminogen activator (u-PA) and plasminogen activator inhibitor type-1 (PAI-1) antigen by ELISA method. Fibrin autography demonstrated fibrinolytic bands at Mr of 100 kD, 70 kD, 62 kD and 55 kD. The 70 kD band was the predominant one. Reverse fibrin autography showed a single fibrinolysis-resistant band at Mr of 40 kD. t-PA was the predominant fibrinolytic protein in ascites and its concentration was 1.5 to 2 times that in plasma (p<0.005). u-PA, t-PA and PAI-1 antigen concentrations were significantly increased in malignant ascites over cirrhotic ascites (p<0.001, p<0.001, p<0.0001). However, the difference in euglobulin fibrinolytic activities was not statistically significant between the two groups. The sensitivity, specificity and accuracy of PAI-1 antigen at the cut-off point of>4.5 ng/ml in diagnosis of malignant ascites were comparable or better to conventional parameters, but those of t-PA antigen and u-PA antigen were not. In conclusion, we observed that fibrinolytic profiles in malignant ascites differ from those in cirrhotic ascites and measurement of PAI-1ag, could be helpful to differentiate malignant and benign ascites.