Oxidative damage from free radicals plays an important role in several diseases such as cancer, Alzheimer's disease, and heart disease. Research indicates that exercise contributes to oxidative stress. Fruits, such as blueberries, are good antioxidants because they contain phenolics that preferentially react with free radicals. Maintaining antioxidant levels by supplementing the diet with blueberries may prevent exercise-induced oxidative damage. The goal of our study was to compare antioxidant levels in sled dogs supplemented with blueberries on blood parameters within 48 h post-exercise. Though the exercise protocol did not cause unusual muscle damage as reflected in plasma creatine kinase and isoprostane levels, blueberry supplementation did elicit significantly elevated antioxidant status in sled dogs post exercise. This suggests that dogs fed blueberries while exercising as compared to dogs fed a control diet while exercising, may be better protected against oxidative damage.