An experiment was conducted using four hundred and eighty day-old straight run broiler chicks. The birds were divided into two groups and fed one of two depletion diets. Depletion diet 1 was low in Se (0.017 ppm.) and adequate in vitamin E (50 I.U./kg.), diet 2 was low in Se. and vitamin E. The two groups remained on these diets for 21 and 15 days respectively until the first signs of exudative diathesis (ED) appeared. During the depletion period blood and tissue samples (3 samples of 3 birds/sample) were obtained at 3 day intervals. Se. levels of 0.120, 0.107, 0.090, 0.073 and 0.041 ppm. were obtained for thigh muscle, kidney, heart muscle, liver and blood respectively at 21 days of depletion on the low Se. adequate vitamin E diet. The same tissues respectively were: 0.083, 0.180, 0.097 and 0.043 ppm. Se. at 15 days of depletion when fed the low Se.-Vit. E deficient diet. The birds fed diet 2 at 15 days of depletion were randomly allotted to 12 pens (16 birds/pen) after which one of four treatments (0, 0.02, 0.04 and 0.08 ppm. added Se. as Na 2 Se0 3 ) was randomly assigned to each pen (3 pens/trt) and fed for 14 days. Triplicate pooled blood and tissue samples were obtained at 3 day intervals as during the depletion period. A significant (P<0.05) response in growth rate and feed efficiency was observed with 0.04 and 0.08 ppm. Se. supplementation. Liver and kidney responded to all dietary Se. supplementation, whereas blood and heart only responded to 0.08 ppm. supplementation. However, skeletal muscle showed no response. Zero, 24, 40 and 70% of birds fed 0, 0.02, 0.04 and 0.08 ppm. Se. respectively were protected from ED during the experiment.