During the past eight months radioactive iron has been used in these laboratories as a tool in the studies of iron metabolism in dogs. This radioactive iron is prepared from the Fe58isotope by deuteron bombardmentIts beta ray activity with a half life of forty-seven days makes this isotope useful as a labeled iron that may be followed in metabolism experiments even after mixture with the ordinary iron in the body. Physiologists will admit that our understanding of iron metabolism is in a parlous state. There are diametrically opposed views relating to almost every phase of iron metabolism in the body. It is fair to state that much of this difficulty relates to methods of iron analysis. Many methods for iron analysis in body tissues,fluids or feces carry errors so large as to render the results useless. If one may state (with allowance for varied opinions) the generally accepted story of the absorption and