We previously reported increased lipid peroxide and decreased alpha-tocopherol levels in the blood of critically ill septic patients. To clarify these results, we investigated lipid peroxidation in experimental septic rats and severely traumatized rats. In septic rats, both platelet count and plasma alphatocopherol decreased significantly, while lipid peroxide in plasma and major organs significantly increased. Serum transaminases also increased significantly. Traumatized rats had a significant but transient decrease in platelet count and a continuous decrease in plasma alpha-tocopherol; lipid peroxide did not change significantly in the plasma but increased significantly in the lung and kidney. Serum transaminases of traumatized rats showed transient increases. Thus, although traumatic stress caused lipid peroxidation similar to sepsis in the major organs, plasma lipid peroxide did not change.