It Is known that free radical is produced by many environmental factors and leads to a variety of pathophysiological lesions often resulting in metabolic Impairment and cell death. Many researches have been performed to limit production of the tree radical. The superoxide dismutase (SOD) has been known to cure of disease relevant to oxygen poisoning. The bis-carboxylethylgemanium sesquioxide (Ge-132) has been suggested to show scavenging activity to precent oxygen damage from lesions. In this study, bioeffects of SOD and Ge-132 for dismutation and scavenging ol the harmful free radical were investigated in Sprague-Dawely rats exposed to the hyperbaric oxygen (HBO 100% oxygen) and hyperbaric ambient air (HAA) under 3.0 atmospheres absolute (ATA) for 180 minutes. When rats were treated with SOD alone anti SOD plus Ge-132 after exposed to HBO, concentrations of potassium and sodium tended to significantly decrease to those in control at levels of p<0.05 and p<0.01, respectively. In contrast, when rats were treated with the SOD only and the SOD only Ge-132 after HBO exposure, creatine phosphokinase significantly increased to the normal level in control. To see whether the SOD anti SOD plus Ge-132 could heal lesions due 4o the tree radicals, rats were exposed to the HBO environment and treated with the SOD alone and SOD plus Ge-132 and then those lung tissues were histopathologically observed using transmission electron microscope (TEM). Lung In exposure to the HAA environment was congested and its alveolar sac was filled with several erythrocytes. Lung to the HBO environment was filled with more erythrocytes than in the HAA. In addition, there were severe lesions of cellular necrosis, hemorrhage, infiltration of inflammatory leucocytes. When rats in exposure to HBO were treated with SOD alone or SOD plus Ge-132, no pathological changes in the lung were observed in comparison with control group. These data indicated that the Ge-132 may synergistically Influence the SOD to remove the tree radicals harmful to tissue.