Intracoronary streptokinase was given to 40 patients with acute transmural myocardial infarction. In 34 of the patients (85%), it resulted in reflow or improved flow. Six patients showed no reflow and six reocclusion within 2 hours. No consistent explanation was found for this resistance to therapy. Five other patients developed reocclusion after 6 days to 11 months, when heparin or warfarin anticoagulation had been stopped. Percutaneous angioplasty at the time of streptokinase infusion was performed in seven, with six successes. Bypass surgery was performed after successful streptokinase administration in eight. Follow-up revealed recurrent ischemia in patients successfully treated with streptokinase alone, but not in patients with successful angioplasty or bypass surgery. Long-term coronary patency after thrombolysis may require careful anticoagulation or a procedure that modifies or bypasses the residual stenosis.