Oxygen free radicals are known to form after reperfusion of ischemic tissue. To test the role and importance of oxygen free radicals in hemorrhagic shock, an animal model of hemorrhagic shock and resuscitation was utilized. Sprague-Dawley rats were anesthetized with halothane and then subjected to approximately 50 per cent blood volume hemorrhage (30 cc/kg), followed by a 60 min shock period. Resuscitation was performed over 1 hour with lactated ringers (LR) at a volume of two times blood loss (60 cc/kg). This model results in a survival rate of 25 per cent over 72 hrs. Using this model, animals were randomized to receive either LR, Superoxide Dismutase-Polyethylene Glycol (SOD-PEG) (15,000 units/kg) with LR or Catalase-Polyethylene Glycol (CAT-PEG) (175,000 units/kg) with LR. The group treated with SOD-PEG demonstrated significantly increased survival rates vs the group treated with LR (67% vs 25%, P = 0.02). The group treated with CAT-PEG demonstrated no significant improvement in survival when compared to the LR-treated group (20% vs 24%). These data suggest that treatment directed toward oxygen free radicals and reperfusion injury may play an important role in hemorrhagic shock resuscitation.