Although the healthcare field is increasingly aware of the importance of free radicals and oxidative stress, screening and monitoring has not yet become a routine test, since, dangerously, there are no symptoms of this condition. Therefore, in very few cases is oxidative stress addressed. Paradoxically, patients are often advised supplementation with antioxidants and or diets with increased antioxidant profile, which ranges from vitamins to minerals and acts against oxidative stress states; even more so, no test is advised to assess whether the patient is under attack by free radicals or has a depleted antioxidant capacity. Oxidative stress i s an imbalance between free radicals (ROS, reactive oxygen species) production and existing antioxidant capacity (AC); living organisms have a complex antioxidant power. A decrease in ROS formation is often due to an increase in antioxidant capacity, while a decrease in the AC may be associated to increased ROS values. But, this is not always apparently so. Test kits for photometric determinations that are applicable to small laboratories are increasingly available.