Thirteen patients with less than 5 hours of the onset of symptoms of acute myocardial infarction underwent selective coronary angiography. Ten of them had angiographic signs of coronary thrombosis. In these ten patients 15 mgs of an acylated streptokinase-plasminogen complex (BRL 26921 Beecham Farmaceuticals) were administered intravenously. Total angiographic recanalization was observed in 7 patients. The coronary arteries involved were the left anterior descending in 4 cases and the right coronary artery in 3. In 8 out of the 10 patients significant diminution of injury pattern in EKG was registered, however in all of them the necrosis pattern supervened. Prolongation of the thrombin and thromboplastin times, as well as an important fibrinogen disminution were documented in all instances. There were not complications related to the administration of the drug. An increase of muscle enzimes was documented in all cases. The follow-up was uneventfull with excellent results in all the patients. This study proves that with IV trombolitic therapy coronary recanalization can be achieved in the mayority of the patients; however there is no question that myocardial infarction finally ocurred. We speculate about the possibility of avoiding infarction by the administration of the drug within the first hour after the onset of the symptoms.