Thrombolytic agents are widely used as first line treatment in severe acute pulmonary embolisms. While their indications are well defined, no controlled trial exists to provide definite evidence of their ultimate effectiveness in terms of mortality. Nevertheless, therapeutic advances and the good results obtained in terms of satisfactory changes in hemodynamic and angiographic parameters have led to renewed evaluation at the present time of the ways in which they are used in thrombo-embolic disease: administration of thrombolytics as repeated boluses in order to decrease the risk of hemorrhagic complications; and extension of the indications of thrombolysis to the venous component of thrombo-embolic disease.