Hypochlorous acid (HOCl), produced by activated polymorphonuclear (PMN) leukocytes, has been reported to depress cardiac function and contractility. Various mechanisms exist for activation of PMN leukocytes during hemorrhagic shock and reperfusion. In order to determine the role of HOCl in hemorrhagic shock and reinfusion, the authors studied the effects of shock and reinfusion on the cardiac function, contractility, blood lactate, blood gases, and creatine kinase (CK) and MB fraction of CK (MBCK) with and without methionine (quencher of HOCl) in anesthetized dogs. Dogs were divided into two groups: Group I, hemorrhagic shock (two hours) and reinfusion (two hours): Group II, hemorrhagic shock and reinfusion with methionine treatment. Cardiac index, mean arterial pressure, and index of cardiac contractility were similar in the two groups during shock. Postinfusion recovery of cardiac function and contractility was better in group II. Increases in blood lactate were similar in the two groups during shock. The rate of return of blood lactate to preshock values after reinfusion was greater in group II. The increases in serum CK and MBCK of the two groups during shock were similar but not significant. Following reinfusion the levels of these enzymes increased significantly, but the increases in group II were less. These results suggest that HOCl produced by activated PMN leukocytes may play a role in cardiac damage during hemorrhagic shock and reinfusion. Methionine may have beneficial effects in the hemodynamic and metabolic recovery and may reduce cellular damage during hemorrhage shock and reinfusion.