Owing to the possible involvement of impaired fibrinolytic function in venous and arterial thrombotic disorders, and the benefit of thrombolytic treatment in the acute stage of myocardial infarction, the fibrinolytic system has attracted increasing interest. In this brief review are discussed recent advances in our knowledge of the regulation of fibrinolysis and the effect in thrombolytic disorders of impaired tissue plasminogen activator release and increased concentrations of the endothelial cell-related plasminogen activator inhibitor. PAI-1. Also discussed are the molecular basis of effective and specific thrombolytic treatment and progress in the search for and development of new, primarily recombinant, fibrin-specific plasminogen activators.