Theoretically, zinc can exert a number of indirect antioxidant functions. Researchers at our laboratory have found evidence to support this concept by studying mild zinc deficiency in rats. This state produces low resistance to chemically induced liver oxidant injury, and it produces high vulnerability of lipoproteins to oxidation. We are building on this work in rats to test a hypothesis in humans that increased zinc intake will protect against oxidant stress in persons with tendencies for both moderate zinc deficiency and high oxidant stress. This hypothesis has been tested in postmenopausal, type 2 diabetic women. A 3-wk supplementation with zinc (30 mg/d as glycine-chelate) raised initially low plasma zinc values to above normal values and increased plasma activities of 5'-nucleotidase. However, the latter values were still well below normal. Lipoprotein oxidation tendencies, a measure of oxidant stress, were not altered by the zinc treatment. A new project has been initiated to determine whether both a higher dose and longer duration of zinc treatment will normalize 5'-nucleotidase activities and affect the indices of oxidant stress. The latter will be considered in terms of both zinc supplementation and supplementation of zinc plus vitamin C, another problem nutrient for diabetic persons.