Abstract THE need for vitamin G by poultry, particularly during the growing and breeding period in the life cycle, has been established by Hauge and Carrick (1926), Norris et al (1933–36), Bethke (1933), Heiman (1935), and others. In poultry feeding, the flavin requirement may be met by feeds from several sources, among which are dairy by-products, yeast products, dry or succulent green feeds, and, under some conditions, by certain packing house and marine products. Dairy by-products especially are used extensively to supply flavin. Heiman, loc. cit., demonstrated the differences which exist in the relative vitamin-G content of various dairy products, particular emphasis having been given to dried skimmilk and dried whey, which are extensively used as poultry feeds. The principal purpose of the study reported here was to determine the relative flavin content of dried buttermilk, another dairy by-product, often used in poultry feeding. PROCEDURE A group of 500 day-old . . .