The adequacy of human milk for low-birth-weight infants remains controversial. In this study, 35 healthy preterm infants with gestational age from 31 to 36 weeks and a birth weight less than 2200 g, were followed until they attained a weight of 2400 g at about 5 to 7 weeks of age. These infants were fed pooled, expressed human milk, partly supplemented with their own mother's milk, at intakes of 185 and 200 ml/kg/day. There were no consistent differences between the feeding groups in the rate of gain in weight, length, or head circumference, in serum total protein, in acid-base status, or in plasma amino acid concentrations. It is concluded that pooled, expressed human milk in volumes of 185 or 200 ml/kg/day produces a postnatal weight gain (196 +/- 6 or 205 +/- 7 g/week, respectively) in healthy preterm infants with a gestational age over 31 weeks which compares to intrauterine weight gain (207 g/week). This growth is achieved without apparent metabolic stress.