Interest in free radical events has stimulated speculation that their disorder may be involved in a number of diseases. The reduction of dioxygen to water involves several active intermediates. The control of this depends on the integrity of an enzymatic system that requires adequate intake of selenium, copper, zinc, and manganese; if their level of intake is low, proliferation of active oxygen metabolites may occur. Targets for attack are DNA, proteins, and polyunsaturated phospholipids. Peroxidation of polyunsaturated phospholipids will result in disruption of membrane architecture. Vitamin E, perhaps with ascorbic acid, can prevent this, and vitamin A and beta-carotene also intervene. The implication of this in the etiology of a number of diseases depends on theory and on evidence linking low intake of the antioxidant nutrients with a high disease incidence. Improvements in epidemiology have resulted in glimpses into what may prove to be links between diet and disease.