1. Iron absorption in rats is increased by dietary iron deprivation.
2. Erythropoiesis in the rat is unaffected by dietary iron deprivation that increases iron absorption by more than a factor of four.
3. Iron absorption is not increased in rats bled of an amount of iron equivalent to that lost in 5 days of iron deprivation.
4. These findings are compatible with the concept that iron-absorption is controlled by depletion of iron from a specific pool, separate from the hepatic and erythrocytic iron pools.
5. Iron absorption in human subjects was unaffected by dietary iron deprivation for 13 days. Reasons for differences between human and rat results are discussed.