Patients with a recent (less than 10 days) proximal deep vein thrombosis of the leg or pelvis are candidates for thrombolysis as the major benefit over heparin seems to be the prevention of the postphlebitic limb, an aim which is still not proven in a satisfactory manner. Nonocclusive thrombi appear to lyse more readily than occlusive thrombi. For this indication the optimal dose regimens for the three thrombolytic drugs (streptokinase, urokinase, alteplase) are not established.