The purpose of this study was to compare growth following hospitalization in preterm, low birth weight infants fed their own mother's milk versus preterm, low birth weight infants of similar weight and gestational age given standard infant formula upon demand. Growth measurements were taken 40, 42, 48 and 56 weeks postconceptual age. A total of 28 healthy, preterm, low birth weight infants completed the study. Seventeen infants received standard infant formula (Similac) and 11 were breast-fed upon demand. Introduction of solid foods was delayed until the infant was greater than 56 weeks postconceptual age. Weight, length, occiptial frontal circumference, mid-upper arm circumference, triceps and subscapular skinfold measurements were obtained at 40, 42, 48 and 56 weeks postconceptual age in our nutrition follow-up clinic. Analysis of variance with feeding as well as age, sex, gestational age at birth, birth weight, birth length and birth head circumference as factors was performed utilizing Duncan's Multiple Range Test. Weight, mid-upper arm circumference, and triceps and subscapular skinfold measurements were shown to be significantly greater in infants fed formula versus human milk from birth to 40 weeks postconceptual age. Gestational age at birth and increasing chronological age was also shown to influence these measures. Statistical significance was less than the one percent level. However, no statistical or clinical differences were found in rates of growth preterm, low birth weight infants fed either human milk or standard infant formula from 40 to 56 weeks postconceptual age. Both feeding groups experienced growth within the 10 to 90th percentiles of accepted infant norms for all parameters. It was concluded that preterm, low birth weight infants allowed to be breast-fed upon demand post-hospitalization experienced acceptable rates of gains from 40 to 56 weeks postconceptual age. Use of commercial formula was not found to be more advantageous than breast feeding.