Studies were conducted to determine the effects of high levels of dietary silver nitrate and copper sulfate on the response of chicks to toxic levels of dietary selenium. Adding 5 ppm or more selenium to a basal stock diet significantly reduced growth rate, and 40 ppm or high significantly increased mortality during the 2-week experiments. Deitary silver or copper (1,000 ppm) counteracted the growth depression and prevented mortality at the higher levels of selenium. Hepatic selenium reached a maxiumum in chicks fed the basal diet with 10 ppm dietary selenium. Hepatic selenium of chicks fed silver was less than that of the control chicks when diets containing 10 ppm or less selenium were fed. Adding copper to the diet resulted in considerable accumulation of selenium in the liver, which was evident even at the lower levels of added selenium. Rseults of an experiment to determine the effects of deitray silver and copper on the distribution of 75-Se administered either orally or in tramusculary showed that silver interfered with absorption of selenium. The results of these experiments suggest that silver modifies selenium toxity both by interfering with selenium absorption and by causing the accumulation of a nondeleterious selenium compound in the tissues. Copper modifies selenium toxicity primarily by causing the accumulation of a nondeleterious compound in the tissues.