Although heparin is the primary drug used to treat pulmonary embolism, its limits include poor prevention of recurrence, and slow and delayed normalization of hemodynamic parameters. Over the past decades, thrombolysis has proved to be the most rapid and effective therapy to normalize hemodynamic parameters and angiographic and scintigraphic indexes of obstruction. Studies conducted up to the present have not, however, demonstrated a significant advantage over heparin with respect to mortality. Moreover, thrombolytic drugs carry a greater risk of hemorrhage than heparin. Various experimental studies have demonstrated that the short-term administration of recombinant tissue plasminogen activator (rt-PA) is more effective and decreases risk of hemorrhage. To our knowledge, only a few uncontrolled clinical studies on bolus thrombolysis with urokinase have been done. Studies comparing a 0.6 mg/Kg bolus of intravenous rt-PA versus the infusion of 100 mg over 2 hours have given conflicting results. Of these, some have demonstrated that bolus administration is safer and more effective while others have provided nearly overlapping results regarding safety and the reduction of pulmonary resistances. One study reports higher mortality in a group receiving 0.6 mg/Kg bolus rt-PA. Until these questions are clarified, administration of thrombolytics in the following doses is advised: streptokinase bolus 250,000 U over 30 min + 100,000 U/hour for 24 hours; urokinase bolus 4400 U/Kg for 10 min + 4400 U/Kg/hour for 12-24 hours; rt-PA 100 mg for 2 hours.