Oxidative stress (free radical generation exceeds antioxidant defense) occurs in many diseases and after exposure to certain chemicals. We automated assays estimating the antioxidant status of serum and lipid hydroperoxide concentrations using the Syva-30R automated analyzer. In this assay, the antioxidant status of serum is measured by its ability to inhibit the generation of free radicals from 2,2'-amino-di-[3-ethylbenzthiazole sulphonate] by metmyoglobin and hydrogen peroxide. The assay for measuring lipid hydroperoxide concentration in serum utilizes the ability of lipid hydroperoxide to generate methylene blue from 10N-methylcarbamyl 3,7-dimethylamino 10H-phenothiazine. Phenytoin is known to initiate oxidative damage to proteins and lipids in murine maternal hepatic and embryonic tissue organelles. Therefore, we measured lipid hydroperoxide concentrations in sera of epileptic patients receiving phenytoin. We observed significantly elevated lipid hydroperoxide concentrations in epileptic patients receiving phenytoin compared to controls. The total antioxidant capacity of sera of epileptic patients was lower than the antioxidant capacity of control sera. We observed poor correlation between the serum lipid hydroperoxide concentration and triglyceride or cholesterol concentration in epileptic patients. We conclude that lipid hydroperoxide concentrations were elevated in sera of epileptic patients.