The effect of intracoronary streptokinase administration (31 patients), verapamil treatment (23 patients) and conventional therapy (27 patients) on the size of the affected area was examined in patients with acute myocardial infarction (MI). Streptokinase was administered in a dose of 250,000-500,000 IU within the first 3 to 20 hours of myocardial infarction, and verapamil, 360 to 400 mg, daily within the first 5 to 12 hours of the attack. The occluded coronary artery was recanalized in response to streptokinase administration in 21 patients. Serial measurements of CPK activity and serum myoglobin levels, and electrocardiographic precordial cartograms demonstrated a reduction in MI size following streptokinase administration. Verapamil had no basic effect on the final size of myocardial lesion, although it improved somewhat the clinical course of the disease.