Free radicals are thought to be implicated in the pathogenesis of various human diseases. A variety of antioxidant defense systems are operative, including enzymatic and nonenzymatic mechanisms. An important source for antioxidants is diet. The most prominent dietary antioxidants are vitamin C, vitamin E and the caritenoids. There is increasing evidence from epidemiological studies, that an increased intake of antioxidants is associated with a diminished risk for several cancers.