Coagulation and fibrinolysis were investigated in 14 claudicants undergoing percutaneous transluminal angioplasty (PTA) for femoropopliteal artery lesions. Cross-linked fibrin degradation products (XL-FDP), tissue plasminogen activator (t-PA) antigen, fibrinopeptide A (FPA), and plasminogen activator inhibitor-1 (PAI-1) activity were measured in peripheral blood. XL-FDP and t-PA increased, and FPA and PAI-1 decreased significantly after angioplasty. XL-FDP increased from baseline 266 +/- 72 ng/ml to 481 +/- 239 ng/ml (p < 0.0005) 30 min after PTA, indicating mural thrombus formation in spite of the significant fall in FPA influenced by heparin. A groin haematoma developed after PTA in 4/6 patients, who received more than 5600 IU heparin and in 1/8 patients receiving smaller dosages. The alterations in PAI-1 showed no correlation with those of t-PA, whereas heparin had a sparing effect on PAI-1 consumption. These findings may indicate that PAI-1 acts as a thrombin inhibitor following deep vessel wall injury by angioplasty. In two patients, who had signs of rethrombosis on the next day, residual FPA was relatively high, XL-FDP peaked at 3530 +/- 1170 ng/ml, and t-PA increased by 2.6 +/- 1.0 ng/ml. The corresponding values in patients with an uncomplicated course were 406 +/- 89 ng/ml (p < 0.0001) and 0.1 +/- 0.5 ng/ml (p < 0.02). We conclude that thrombin promotes activation of coagulation and fibrinolysis in femoropopliteal PTA. Instability between these counteracting systems resulting in thrombosis is not prevented by conventional heparin administration at dosages causing bleeding complications.