Free radicals and Reactive Oxygen Species (ROS) are highly reactive molecules generated by normal cellular processes, environmental stress, and UV irradiation. ROS react with numerous cellular components damaging DNA (but also carbohydrates, proteins, and lipids) and cause cellular and tissue injury. Measuring antioxidative capacities of biological fluids, cells, and tissue such active molecules is becoming more and more important in the pharmaceutical industry and in academic laboratories. Let’s focuse here on 2 robust methods.