In breast-fed infants bifidobacteria is predominant, counts of Escherichia coli is low, and other bacteria is rarely present. Infants receiving Iron fortified cow-milk preparation have high counts of Escherichia coli, counts and isolation frequency of bifidobacteria are low and other bacteria are frequently isolated. In those on unfortified cow-milk preparation isolation frequency of Escherichia coli, bifidobacteria and bacteroides is comparable with that in breast-fed infants; however, counts of Escherichia coli is high.