Milk intake and growth in 45 exclusively breast-fed infants were documented during the first 4 months of life. Energy and protein intakes were substantially less than current nutrient allowances. Energy intake declined significantly from 110 +/- 24 kcal/kg/day at 1 month to 71 +/- 17 kcal/kg/day at 4 months. Protein intake decreased from 1.6 +/- 0.3 gm/kg/day at 1 month to 0.9 +/- 0.2 gm/kg/day at 4 months. Infant growth progressed satisfactorily, compared with National Center for Health Statistics standards. A reevaluation of energy and protein intakes and allowances during infancy is merited.