Titers of antibody against Escherichia coli in human milk and in the sera of 11 breast-fed infants, 6 bottle-fed infants and 9 infants in the post-weaning period were measured by the passive hemagglutination method. High antibody titers were observed in human milk in the first 4 days after parturition, but the titer decreased rapidly thereafter. None of the healthy, breast-fed infants had detectable serum antibodies, while a breast-fed infant with a perianal E. coli abscess had antibodies. On the other hand, 4 of the 6 bottle-fed infants and all of the 9 infants in the post-weaning period had antibodies. The significance of these results was discussed.</p
