Ten patients with acute myocardial infarction (AMI) underwent coronarographic studies before, immediately after and ten days after an intravenous infusion of 1 500 000 I.U. streptokinase (STK). Mean time between onset of symptoms to initiation of STK infusion was 03 hours 34 minutes. Occlusion of the infarct-related vessel was present in all of them and successful thrombolysis was obtained in 8 of the patients. Systemic fibrinolytic activity was present in 9 patients, one of whom required a transfusion of blood because of severe bleeding. At ventriculography, the global left ventricular ejection fraction and the regional ventricular ejection fraction, whatever the area involved, showed no significant improvement 10 days after the procedure. This suggests that high-dose intravenous STK in AMI, although causing an effective thrombolysis, does not seem to improve early myocardial function.