1. 1. The object of this study was to compare the pattern of red cell phosphates at different ages of development of two members of the order of non-flying ratite birds, the emu and the rhea, with data which had been obtained on examples from four orders of flying birds: chick and others ( Galliformes). duck ( Anseriformes), sea gull ( Charadriformes) and pigeon ( Columbiformes). Limited information is also given on another ratite, the ostrich. 2. 2. Distinctive features of the flying birds were a high concentration of inositol pentaphosphate (IP5) in the adult, with only traces of other inositol polyphosphates, and a brief appearance of a high concentration of 2,3-diphosphoglycerate (DPG) late in embryological development. 3. 3. Maximum IP5 in red cells of adult emu, rhea and ostrich was only about half of that found in other birds. 4. 4. Inositol tetraphosphate was absent in the emu. was one quarter of the IP5 in the rhea and twice as much as the IP5 in the ostrich. 5. 5. No DPG was found in red cells of emu and rhea at any age; however, the ostrich had a high concentration in red cells of a late embryo.