• A number of recent studies have reported reduced growth velocity among breast-fed infants, as compared with standard growth curves. Contradictions between these and previous studies of breast-feeding have been difficult to resolve because of methodological problems, particularly supplementation of breast-feeding with other nutrients. In the present study, 33 term infants, exclusively breast-fed for six months, showed significantly slower rates of growth compared with data from the National Center for Health Statistics (NCHS). Between birth and 6 months of age, these infants lost an average of 20 percentiles in weight for age and 30 percentiles in length in relation to the NCHS population. We discuss these findings in terms of the appropriateness of the NCHS data as standards and the adequacy of exclusive breast-feeding for providing optimum growth through 6 months of age.