Weekly increments of length, weight, head circumference, and skinfold thickness in response to a series of dietary changes were measured in 108 healthy infants who weighed less than 1.3 kg at birth. The serial manipulations included prevention of late metabolic acidosis, increased caloric intake, and calcium, sodium, and phosphorus supplementation. The study comprised four phases; the infants were divided into ten groups according to dietary regimen. AGA and SGA infants were studied separately. Growth in length was primarily influenced by a change to a formula providing a higher caloric intake and a 60:40 whey protein/casein ratio. Correction of late metabolic acidosis, sodium, and phosphorus supplementation had minor additive effects on growth in length. Increased caloric intake also influenced growth of head circumference, but only in AGA infants. Only the sodium intake was shown to influence body weight increments significantly with the range of caloric intake used in the study (132 to 160 calories/kg/day).