Experiments in animals have shown that coronary artery reperfusion limits the extent of myocardial damage and brings about late return of regional contraction and overall left ventricular function over a period of several weeks. Such studies provide a basis for optimism that similar effects can be demonstrated after thrombolytic treatment in man, and such functional contractile recovery should provide an important end point in clinical investigations. However, before the initiation of a large-scale clinical trial, adequate methods for determining salvage of myocardium must be identified, and since changes in such measures may be small, the use of mortality as an end point should also be considered. In addition, the possibility of having two treatment groups to compare intracoronary and intravenous modes of therapy should be examined. Based on the growing number of uncontrolled clinical reports concerned with the success of intracoronary thrombolysis in restoring vessel patency and preliminary data on morbidity, mortality and potential improvement in left ventricular function with this procedure, planning for a randomized clinical trial sponsored by the National Institutes of Health is warranted.