In living cells, reactive oxygen species (RIDS) are formed continuously as a consequence of metabolic and other biochemical reactions as well as external factors. Antioxidant defence systems to counter this cannot provide complete protection from the noxious effects of ROS which includes oxidative damage to DNA. Experimental studies in animals and in vitro have suggested that ROS are an important factor in carcinogenesis. There is a crucial balance between free-radical generation and antioxidant defence as a force in disease prevention. An imbalance between protection against free radicals and their generation can be associated with the pathogenesis of a wide variety of diseases. Since oxidative/electrophilic stress is generally perceived as one of the major causes for the accumulation of mutations in the genome, antioxidants are believed to provide protection against cancer. A number of natural and synthetic antioxidants are known to retard chemical carcinogenesis in experimental animal models, and epidemiological studies suggest that a diet rich in plant products containing natural antioxidants may be a deterrent to carcinogenicity. Some prospective assessment of the effect of supplemental antioxidants such as vitamin C, vitamin E, selenium and carotenoids can be recommended for the maintenance of health and the prevention of disease as well as a diet rich in fruit and vegetables.