The toxicity of hemoglobin (Hb) solutions is related, at least in part, to the generation of oxygen free radicals with consequent induction of lipid peroxidation. The present study was designed to examine whether selenium (Se) may prevent the oxidative damage observed after Hb administration. Three groups of rats were compared; (I) the negative control group receiving autotransfusion; (II) the positive control group with replacement of 40% total blood volume (TBV) with modified bovine Hb solution; and (III) the experimental group which received dietary supplemented selenium (Na2SeO3) in daily doses of 5 micrograms.kg body wt-1 in drinking water, 4 days before and 3 days after administration of Hb solution in the same volume as in group II. Three days after Hb injection, all animals were sacrificed. Oxidative stress was determined by measuring conjugated dienes (CD) and thiobarbituric acid reactants (MDA) in homogenates of the perfused liver, heart, lungs, kidney, brain and plasma. Additionally, the 45k x g supernatants of the organs homogenates and plasma were assayed for the antioxidant enzymes activity: superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px) and the intracellular level of reduced glutathione (GSH). Also, a measurement of nonprotein bound intracellular free iron (Fe) and tissue Se concentrations was performed. Simultaneously, injury dysfunction of vital organs was assessed by the measurement of plasma LDH, SGPT, creatinine, blood PaO2 and by histopathological studies. Results indicate that the exchange transfusion with Hb solution introduced significant increases in CD and MDA formation, particularly in the liver and heart tissues, and in plasma. While the values of the SOD and CAT in the liver and heart tissue were generally altered, the SOD/CAT ratio was also increased. After the Hb injection, activity of GSH-Px remained unchanged and was associated with significant depletion of GSH. The plasma levels of SGPT and LDH were increased, but the creatinine and PaO2 was similar to that of the control and corresponded with histopathological findings. The liver and heart intracellular free Fe was found to be higher than that of control. Treatment with Se was very effective in the prevention of oxidative damage introduced by Hb. Full protection from MDA formation was noted in liver tissue (p < 0.001). Also, plasma levels of MDA, SGPT and LDH were significantly decreased and appeared similar to that of the control group (I). Treatment with Se increased liver (p < 0.05) and plasma (p < 0.1) level of GSH-Px.(ABSTRACT TRUNCATED AT 400 WORDS)