Diabetes mellitus is not simply a disorder of glucose homeostasis, but is also accompanied by various degenerative manifestations, such as cardiovascular disease and microvascular lesions leading to retinopathy and glomerulopathy. These events may be related to the hyperproduction of free radicals and to a deficiency in available antioxidant systems like low enzyme activity or deficient micronutrient status. To test the feasibility of this idea, we compared the activities of plasma catalase and glutathione peroxidase, as well as the latterÕs cofactor, selenium in diabetics (n=14) and age-matched healthy controls (n=12). The antioxidant enzyme activity in the diabetics was generally lower than in the controls. The following results were obtained: (mean±SEM, controls and diabetics, respectively): plasma catalase 154.02±13.71 kU/L and 114.31±17.60 kU/L (p