The possible antagonistic effects of different dietary concentrations of copper (1.3-200 mg/kg), cadmium (1-5 mg/kg), iron (20-500 mg/kg), molybdenum (0.3-50 mg/kg) and manganese (0.2-200 mg/kg) on selenium utilization by the rat were studied by the measurement of the absorption and organ distribution of dietary selenium as [75Se]selenite and by effects on organ glutathione peroxidase (GSH-Px: EC 1.11.1.9) activity. Although a high concentration of copper (200 mg/kg) in the diet did not alter the percentage absorption and total-body retention of doses of 75SeO3(2)- by rats, after such treatment tissue 75Se distribution was changed and was lower total selenium in some tissues. After copper treatment (200 mg/kg diet) GSH-Px activity of liver, testis, kidney and whole blood was also lower. Dietary cadmium, iron, molybdenum and manganese at the concentrations investigated had no significant effects on selenium metabolism. Thus it is unlikely that copper, cadmium, iron, molybdenum and manganese at normal dietary concentrations will have a major effect on selenium metabolism in the rat, especially if adequate amounts of selenium are being consumed.