The sources of free radicals and antioxidant defence systems in living organisms are reviewed. Attention is focused on the role of dietary lipid oxidation products and antioxidants to maintain balance between factors promoting free radical mediated oxidation and the antioxidant defence mechanisms. Particular attention is paid to the influence of intake of vitamins with oxidative properties (vitamin C, vitamin E and ß-carotene) and polyphenols compounds in the prevention of coronary heart disease and cancer.