An experiment was carried out to investigate the effect of vitamin E on the metabolic impact of heat stress in hens. The study included 150 Leghorn laying hens, which were assigned to 2 groups and initially subjected to the same environmental conditions. Diets were based on standard layer rations with 30, 80, or 105 mg of vitamin E/kg. All birds were kept in 45% relative humidity (RH) and at a room temperature of 21 degrees C for first 3 weeks for adaptation. In the fourth week the temperature and RH were increased to 35 degrees C and 65%, respectively, in the experimental group. Before, during, and after exposure to heat stress blood samples were taken from both groups. Vitamin E analyses were determined by HPLC. Biochemical parameters were analyzed spectrophotometrically. Statistically significant (P <= 0.05) increases in plasma malondialdehyde (MDA), erythrocyte MDA, glutathione peroxidase (GSH-Px), catalase (CAT), superoxide dismutase (SOD), and egg yolk MDA concentration, and a decrease in plasma vitamin E were seen in the experimental group during heat stress. Egg quality parameters also decreased in the experimental group during heat stress. Dietary supplementation with higher levels of vitamin E alleviated some of the metabolic consequences of heat stress; there was no evidence of a beneficial effect on egg production during heat stress within the dietary range investigated.