Generation of free radicals and subsequent lipid peroxidation have been proposed to contribute to delayed tissue damage following traumatic spinal cord injury (SCI). Ubiquinols (reduced coenzyme Q), ascorbate (vitamin C), and alpha-tocopherol (vitamin E) are endogenous antioxidants; decreases in tissue levels of these compounds may, therefore, reflect ongoing oxidative reactions. In the present studies, alterations in tissue levels of ubiquinol-9 and -10, ascorbate, and alpha-tocopherol were examined after SCI of varying severity in the rat. Levels of alpha-tocopherol did not change significantly after injury. Ascorbate and ubiquinol levels were decreased after trauma. Changes in tissue levels of ubiquinol, but not ascorbate reflected the degree of trauma. Thus, ubiquinol levels may provide a useful marker of the oxidative component of the secondary injury response.