SUMMARYGroups of rats were injected with “Imferon” and with red cells to increase the storage iron. After seven weeks a tracer dose of iron‐59 was given to each animal and three weeks later the percentage of the dose in the blood, liver and spleen was determined by radioassay. Compared with control animals, decreased absorption of iron‐59 was found in the rats loaded with “Imferon” and with red cells. This suggests that the size of the iron stores is an important factor regulating iron absorption. Some of the unrecovered red cell iron was in tissues other than those assayed, but a large amount was probably lost from the body during the experimental period. These considerations also applied to the “Imferon” injected animals, but in addition some of the “Imferon” was still present in the mesenteric lymph tissues.