Intracoronary application of thrombolytic agents, particularly streptokinase, can recanalize arteries that had been totally occluded in patients with evolving acute myocardial infarction (AMI). Numerous uncontrolled trials have testified to the effectiveness of thrombolytic therapy in most patients in reestablishing flow to the infarct-related coronary artery. Follow-up of patients in whom reperfusion has been established has often demonstrated small but significant increases in the left ventricular ejection fraction. In contrast, in other patients in whom thrombolytic therapy failed to reopen the occluded vessel, the left ventricular ejection fraction usually does not change during follow-up. In most reported uncontrolled trials, few complications are described and the mortality rate in patients treated by this therapy may be lower than expected. These data have been used as the basis for widespread application of this technique in many catheterization laboratories around the world. Our initial experience at the University of Florida in 23 patients has not been as successful as other uncontrolled trials previously reported. Reperfusion was accomplished in only 12 patients. Of 17 who survived their AMI, only five demonstrated an improved left ventricular ejection fraction of at least 10%. Serious complications, including bleeding from catheterization sites or allergic reactions to streptokinase, occurred. Controlled trials to critically evaluate this new therapy are needed and are in progress.