Breast feeding is thought to result in a lower incidence of iron deficiency than does the use of unfortified cow milk forumalas, but there is scant documentation for this belief. The relationship of breast and cow milk feeding to absorption of iron and to iron status was investigated in a total of 45 term infants at about six months of age. Iron absorption was measured by total body counting. Laboratory assessment of iron status was based on the serum ferritin, hemoglobin, mean corpuscular volume, and transferrin saturation. The results indicated that infants fed breast milk during the entire first six to seven months of life attained greater iron stores than did those fed a cow milk formula. Breast-fed infants absorbed an average of 49% of a trace dose of extrinsic iron administered during a breast feeding in contrast to about 10% reported to be absorbed from cow milk under similar conditions. The data indicate that term infants who are breast fed may not require routine administration of supplemental iron.