Reactive oxygen species (free radicals) play an important role in carcinogenesis. Extensive antioxidant defense mechanisms counteract free radicals in mammalian cells. Oxidative stress is a disturbance in the balance between the production of free radicals and antioxidant defenses. There is direct evidence that oxidative stress and lipid peroxidation (LPO) are linked to the etiology of breast cancer. The increasing global incidence of breast cancer emphasizes the need to understand the various mechanisms involved in breast tumorigenesis. The present study was undertaken to investigate the oxidative stress and antioxidant status in the blood samples of patients with breast cancer.