During the past 2 years, streptokinase has been used to treat subclavian or axillary vein thrombosis in seven patients of whom two were considered "effort" thromboses and five resulted from use of a central venous catheter. All patients had venography performed before treatment to document the thrombosis, and venography was repeated after streptokinase therapy to determine the status of clot dissolution. Streptokinase was given either systemically or in a lowered dose locally, with low-dose therapy chosen whenever a catheter could be threaded up to the clot through an antecubital vein. Although all seven patients had resolution of their clinical symptoms, only one had complete dissolution of the thrombus. The failure of streptokinase to completely dissolve the thrombus suggests that, although apparent clinical improvement can be achieved after streptokinase infusion, treatment of the underlying cause, whenever possible, may be necessary if complete resolution of the thrombus is to occur.