Only patients with first onset acute DVT will be accepted. Acute DVT-LE must be documented by ultrasonography or venogram and will be defined as thrombosis of a major deep vein segment above the popliteal vein less than 14 days since onset of symptoms or diagnosis. Extension of thrombosis from the popliteal vein into calf veins is acceptable, but isolated calf vein thrombosis will not be treated under this protocol, as the benefits of thrombolytic therapy do not outweigh the risks.