Physiological stress induced by environmental factors results in an up-regulation in the antioxidant defense mechanism in cotton. In this study, DNA damage was determined by analyzing 8-oxoguanine which is a strategic marker on DNA caused by Reactive Oxygen Species (ROS) such as superoxide (O₂^•-), hydrogen peroxide (H₂O₂) and hydroxyl radical (•OH). During oxidative stress, abasic sites such as 8-oxoguanine are produced primarily by •OH which correlate to DNA damage. If ROS production exceeds antioxidant processing capability, stress occurs. Superoxide levels have been shown to be higher in NaCl-sensitive callus as compared to NaCl-acclimated callus. Under normal physiological conditions endogenous ROS can produce around 200,000 base lesions per cell per day. The NaCl-acclimated cotton callus (150mM NaCl) was found to have a nine-fold less basal DNA damage level compared to the control (0mM NaCl) cotton callus. These observations are synchronous with previous studies which demonstrated an up-regulation of antioxidant enzymes in NaCl-tolerant callus.