The weights and heights of 384 breast-fed and bottle-fed infants were studied during the first year of life. The growth of breast-fed infants was superior to that of bottle-fed infants in both sexes. The mean weights and heights of breast-fed male infants were similar to the Harvard standard up to 28 weeks of age. The growth of breast-fed female infants was only parallel to the Harvard standard up to 16 weeks of age, their measurements being lower than Harvard standard from birth, the differences increasing with increasing age. While none of the breast-fed infants suffered severe malnutrition 6% of bottle-fed infants were marasmic at one year of age. Breast milk fulfills the nutritional requirements of infants for four to six months after birth but supplementary feeding is necessary thereafter to maintain optimal growth. Bottle-fed babies are prone to undernutrition because of inadequate calories offered. This risk can be avoided by providing adequate nourishment.