Forty patients (mean age = 56 +/- 17 years) hospitalized for proximal venous thrombosis of the lower limbs of over 7 days duration were treated with fibrinolytic drugs: streptokinase (SK) 28 cases, urokinase (UK) 12 cases. The efficacy of fibrinolytic therapy was assessed by phlebography before and 4.5 +/- 2 days after onset of treatment. A phlebographic score based on Marder's method was used to quantify the thrombosis. The repermeabilisation of venous branches was also noted. The results show an overall efficacy of fibrinolytic drugs: total lysis was observed in 6 patients and partial thrombolysis in 18 patients. The overall reduction of the phlebographic score was -2.8 +/- 3.9, and the rate of repermeabilisation of the femoral veins was over 50%. Streptokinase seemed to be the most effective drug. Better results were obtained when the thrombosis was treated early and was proximally situated, but good results were also observed in cases of total thrombosis with a floating thrombus. Effective fibrinolysis was observed in thromboses of up to 3 months duration. There was no correlation between biological efficacy and clinical symptoms. In conclusion, fibrinolytic drugs are partially effective in semi-recent or chronic venous thrombosis and their usefulness should not be overlooked, especially in cases of persistent thrombosis of the femoral veins.