Iron storage in the first 5 years of life has been evaluated by chemical determination of "hemosiderin" iron concentration of samples of liver from 58 selected autopsies; histological preparations of the liver of these patients have been stained by the Prussian blue reaction. Similarly prepared histological sections of particles from 109 bone marrow aspirates have been studied. It was not possible to identify normal variations in the content of iron in the bone marrow by the study of such histologic preparations, nor could iron deficiency states he differentiated from the normal by the bone marrow findings using this technique. The normal fall in hemoglobin concentration during the first 2 months of life is associated with a high concentration of storage iron in the liver. Iron deficiency anemia, most commonly encountered during the second year of life, occurs during that period in which the hemosiderin concentration of liver is lowest and storage iron reserves are minimal.