The objectives of this study were to examine the growth pattern of healthy infants who were fed human milk exclusively for > or = 5 months and its relationship to intakes of milk, energy, and zinc. Monthly anthropometric measurements were obtained on 71 infants through 7 months of age and on 43 through 9 months. Milk zinc concentrations were determined and milk intake was measured by 3-day test weighing. Mean (+/- SD) calculated energy intake from human milk was 106 +/- 20, 79 +/- 11, 70 +/- 10, and 57 +/- 12 kcal/kg per day at 2 weeks and 3, 5, and 7 months of age, respectively; intake from milk plus solids was 70 +/- 13 kcal/kg at 7 months. Zinc intakes from human milk were 2.3 +/- 0.68, 1.0 +/- 0.43, 0.81 +/- 0.42, and 0.52 +/- 0.31 mg/day at these points. The maximum mean weight-for-age percentile for both sexes was 62 at 2 months; the mean percentile declined to 33 by 7 months and to 25 by 9 months of age. Mean length-for-age percentile declined from 43 at 2 weeks of age to 28 and 26 by 7 and 9 months of age, respectively. Energy intake at 2 weeks of age was positively associated with the weight increment from 2 weeks to 7 months of age (p = 0.003) and with a change in weight-for-age z scores from 2 weeks to 3 months of age (p = 0.028). Mean energy intakes of healthy breast-fed infants are lower through the first 7 months of life than current recommendations. Zinc intakes of breast-fed infants are likely to be adequate, on average, through 5 months of breast-feeding but subsequently are marginal without the introduction of weaning foods. Revision of standards for growth based on observations in breast-fed infants may be appropriate, but the possibility of growth-limiting nutrient deficiencies should also be investigated.