Purpose : To evaluate the effectiveness and safety of the modified pulse-spray method using Urokinase (UK) insubacute and chronic thrombotic arterial occlusion. Materials and Methods : Modified pulse-spray methods using UKwere performed in seven patients with subacute (1week-1month) to chronic (1 month-5years) occlusive sysmptoms suchas limb pain, claudication and impotence. Angiographic examination revealed thrombotic occlusion of the aorta,common iliac arteries, brachial arterio-venous hemodialysis graft and femoro-popliteal bypass graft. The patientsunderwent thrombolysis using modified pulse-spray and additional constant infusion of UK. In the presence ofunderlying stenosis or organized clots, balloon angioplasty or stent placement was performed. Results : Completelysis was obtained in five of seven patients. For initial lysis, the mean dose of UK was 420,000 units, and themean modified pulse-spray time was 50 minutes. Mean total dose of UK and mean total time for complete lysis were800,000 units and 161 minutes, respectively. Thrombolysis of the femoro-popliteal bypass graft failed due tosevere occlusion of the distal anastomosis. Partial lysis was achieved in one patient with aorto-iliac occlusion,but further thrombolysis was stopped due to bleeding at the puncture site. Conclusion : The modified pulse-spraymethod using UK is effective in treating subacute and chronic arterial thrombotic occlusion. It augments thespeed, safety and efficacy of thrombolysis. When underlying stenosis or organized clots remain after thrombolysis,balloon angioplasty or stent placement would be helpful.