Storage trials have been conducted on a large number of roller and spray-process whole milk powders. Accelerated tests at 65 °C. were found to give an accurate indication of the relative keeping qualities of the samples. Wheat germ oil antioxidants were found effective in inhibiting deterioration due to copper. Reducing substances that develop in milk powders during storage in a moist atmosphere or at elevated temperatures are strong antioxidants and may offset the effect of added antioxidants. The riboflavin content of several powders with a high concentration of reducing groups decreased appreciably during storage.