We assessed the efficacy of local fibrinolytic therapy in 35 axillary-subclavian vein thromboses (SVT) that occurred in cancer patients with percutaneous central venous catheters (CVC). These catheters were indwelling for a median of 1 month (range, one day to 10 months) before thrombosis developed. Urokinase was administered at a dose of 500 to 2,000 U/kg/h. Complete lysis occurred in 25 of 30 thrombi that were directly infused, after a median of four days. Complete lysis occurred in one of 12 thrombi that could not be directly infused with urokinase and in two of six with associated phlebitis. Eighty-one percent of the thrombi that were symptomatic for less than 1 week before treatment resolved, compared with 56% present for longer than 1 week. Sixteen patients who had complete (12) or partial (four) thrombolysis did not have their CVCs removed. All four patients with partial thrombolysis had recurrent thrombosis at a median of eight days (range, one to 90). Only two patients who had complete thrombolysis had recurrent thrombosis, at 8 and 16 months. Only minor hemorrhagic toxicity was seen.