To evaluate effects of histochrome on severity of reperfusion damage in opening of the coronary artery in patients with acute myocardial infarction (MI).86 acute MI patients were randomized into three groups. 26 patients of group 1 A received 100 mg histochrome 10 min before and 1 hour after intravenous bolus administration of thrombolytic streptokinase; 20 patients of group 1 B received histochrome by the same scheme on the disease day 1 followed by 100 mg/day for 10 days; 40 control patients have undergone thrombolysis without prophylactic histochrome.In the control group ventricular extrasystoles (VES) arose in 100% patients, in groups 1A and 1B--in 27%. The same picture was observed in relation to episodes of accelerated idioventricular rhythm. Coronary reperfusion was accompanied by fast dynamics of ST segment and ORS complex in the control group. MI focus measured by the Selvester ECG method was less in histochrome groups. After myocardial reperfusion malonic dialdehyde in the serum rose 6 times in the control groups and was slightly elevated in groups 1A and 1B.Preventive administration of histochrome before thrombolytic therapy to reperfuse myocardium diminishes reperfusion damage: inhibits activity of lipid peroxidation and development of necrosis focus in acute period of MI.