In this prospective study, we have documented the limited usefulness of thrombolytic therapy in the management of all patients with arterial occlusion of the lower extremities. We have also emphasized the significant rate of recurrent thrombosis unless an underlying obstructive lesion is corrected surgically after clot dissolution. Because thrombolytic drugs can lyse clots of a duration of several weeks, we recommend consideration of fibrinolytic therapy for subacute graft occlusions and segmental arterial thromboses. In such instances, thrombolysis is likely to reveal a focal underlying lesion that is correctable by a limited anastomotic revision or balloon angioplasty. Without fibrinolytic therapy, these older occlusions generally require more extensive bypass grafting or graft replacement. In contrast, we are less enthusiastic about thrombolytic therapy for distal small vessel thrombosis or embolism because complete clot lysis was achieved in only one of five patients. The primary problems with regional arterial low dosage thrombolytic infusions are bleeding at the angiographic catheter entry site and distal thromboemboli of the lysing clot. These difficulties may discourage wide acceptance of fibrinolytic therapy. However, they can be minimized by careful technique. Although its usefulness is limited and complications are common, catheter directed arterial low dosage thrombolytic therapy can be an important initial step in the diagnosis and treatment of selected arterial occlusion of the lower extremities.