Reperfusion of the infarct vessel by a combination of intravenous and intracoronary infusion of streptokinase succeeded in 66 of 120 patients with acute transmural infarction in whom the infusion had been started less than six hours after onset of symptoms. The recanalization attempt failed in 26, and 28 were treated conventionally. Size of the infarct was determined by 201Thallium scanning before and 48 hours after the acute treatment phase. Cox analysis indicated that successful recanalization had a significantly positive effect on the long-term prognosis compared with failed thrombolysis or conventional measures. The perfusion defect (as measured by 201Thallium scan) was identical in all three groups, but after successful recanalization with streptokinase it was significantly smaller than in the other two groups. The improved long-term prognosis is presumably due to a decrease in the size of the infarct.