The physiology of thrombi and the pharmacology of thrombolytic drugs are under active study and improved regimens for the dosing of thrombolytic agents have been developed. In the setting of myocardial infarction, recently reported differences among thrombolytic agents have been slight, including the frequency of thrombolysis-associated hemorrhagic stroke following tissue plasminogen activator or strepto-kinase. In the setting of ischemic stroke, recanalization rates following intravenous tissue plasminogen activator have been modest and at least partly dependent on clot size. Conclusions regarding clinical benefit will depend on the results of multicenter randomized trials that should available in 1995. Studies of locally administered intra-arterial thrombolytic therapy demonstrate high rates of clot lysis, but clinical benefits have yet to be established. The results of randomized trials will be important in clarifying any cause-effect relationships between thrombolytic therapy and symptomatic and asymptomatic intracranial hemorrhage. Thrombolytic therapy in the study of subarachnoid hemorrhage is under active investigation.