Cement dust has been found to be a source of selenium when included in the rations of sheep. In the work reported, rations including 3% by weight of cement dusts were fed to sheep for 165 days. The dust were taken from 3 collectors located at progressively greater distances from the coal-fired end of the kiln. Selenium levels and blood and tissues of the animals fed the cement dusts increased significantly above those of the control sheep. No tissue abnormalities were observed in animals receiving any of the treatment rations. The source of selenium is believed to derive from its content of fly ash as a result of the coal combustion during cement manufacture.