The aim of the study was to analyze the oxidative stress response after severe burn injury. We studied the effect of two methods of fluid resuscitation regimes on the oxidative stress reaction. Sixteen patients were involved in the study. Inclusion criteria were the presence of flame burn injury affecting >20% of BSA and in-hospital fluid resuscitation started within 3 hours after injury. Patients were randomly assigned into two groups. In the first group (n=8), the fluid resuscitation was guided by the hourly urine output and in the second (n=8), by the intrathoracic blood volume index. Blood sample was taken from the patients at admission and on the following five mornings. White blood cell count normalized by the third day in both groups, but the relative number of granulocytes and lymphocytes significantly (P<.05) diverged between hourly urine output and intrathoracic blood volume index groups from the fourth day of trauma. Plasma malondialdehyde level (P<.05 vs control population), reactive oxygen species production in whole blood (P<.05 vs control population), and catalase activity were elevated, whereas glutathione, plasma sulfhydryl groups level (P<.05 vs control population), and superoxide dismutase enzyme activity lowered in both groups. Our results confirmed that burn injury induces pronounced oxidative stress. The main finding is that fluid resuscitation regimes have different impact on prooxidant status, mainly on the granulocyte function but not on the changes in endogenous antioxidants in burned patients.