We propose to: a. Evaluate further the absorption and bioavailability of carbonyl iron powder in rats using radiolabelled material. Is the absorption of carbonyl iron powder influenced by the status of iron stores? Is the material absorbed when baked into bread? If so, how does this absorption compare quantitatively with that of ferrous sulfate added to bread? Is carbonyl iron powder the optimal form of reduced iron for food fortification? b. To compare the absorption of ferrous salts (ferrous sulfate) and iron-chelates (ferrous ascorbate, ferric-fructose, ferric-NTA) in normal, anemic and iron-loaded animals. Are iron-chelates absorbed more efficiently than ferrous salts? Is the absorption of chelated iron modified by the status of iron stores or is absorption independent of iron stores? Will long term feeding experiments using iron-chelates result in hemochromatosis in the rat? c. We shall study the toxicity of iron in rats using an LD-50 oral dose of ferrous sulfate to learn how various states of iron repletion may modify the lethality of the LD-50. Are iron loaded animals protected from the lethality of an LD-50 of ferrous sulfate and are anemic animals more susceptible? If iron loading protects the animal against the absorption of lethal amounts of ferrous sulfate, we will determine the site in the mucosa at which the "block" asserts itself using oral radioiron. By counting the washed gut and carcass separately, it may be possible to localize such a "block" to iron absorption as residing within or beyond the epithelial cells. We will determine the time required for such a "block" to be established.