The role of antioxidants in the maintenance of health and prevention of disorders and diseases has received much attention. Above all, the action and effects of natural antioxidants contained in foods, fruits, spices, beverages and dietary supplements have been the subjects of extensive studies. The capacity of antioxidants has been assessed by various methods, but they often give inconsistent and conflicting results. Animal and human studies do not always support the beneficial effects of antioxidants and the methods for assessment of antioxidant effect are critically needed. In the present article, the methods of assessment of antioxidant capacity are critically reviewed.