This study was conducted to determine the serum and milk levels of thiobarbturic acid-reac- tive substances (TBARS), nitric oxide (NO), superoxide dismutase (SOD), glutathione peroxi- dase (GSH-Px), vitamin E and selenium, IL-4 and IL-6 in lactating dairy cows affected with bloody milk using commercially available ELISA kits. Milk and whole blood samples were collected from 60 cows affected with bloody milk and 20 apparently healthy cows for control. In the serum, levels of GSH-Px and SOD were significantly (p˂0.05) higher in healthy cows compared to cows affected with bloody milk while the levels of TBARS and NO were significantly (p˂0.05) higher in affected cows. In the milk, levels of SOD, TBARS and NO were significantly (p˂0.05) higher in affected cows. In the serum, levels of vitamin E were significantly (p˂0.05) lower in affected cows compared to healthy cows, while no significant changes were observed in the levels of this vitamin in the milk between healthy and affected cows. In the serum, levels of selenium were significantly (p˂0.05) lower in affected cows while in milk, selenium levels were significantly (p˂0.05) higher in affected cows compared to healthy ones. Levels of IL-4 were significantly (p˂0.05) lower in the serum and milk of affected cows compared to healthy cows while levels of IL-6 were significantly (p˂0.05) higher in both serum and milk of affected cows. Results of this study suggest a possible role of oxidative stress in the pathogenesis of bloody milk in dairy cows.