Twenty very low birth weight infants (birth weight < 1500 gm) were assessed to compare the clinical effects of breast and bottle feedings. The infants started breast-feeding during the same week that they started bottle feedings. Five breast-feedings and five bottle feedings for each infant were observed. Axillary temperature and weight before and after feedings were measured, and oxygen saturation, respiratory rate, and heart rate were monitored and recorded every 2 minutes during the feeding periods. The results showed no difference in oxygen saturation during breast-feeding (p = 0.056) but a lower incidence of oxygen desaturation (< 90%) (21% vs 38% in breast-feeding vs bottle feeding, respectively; p < 0.025). Infants with bronchopulmonary dysplasia had higher oxygen saturation during breast-feeding than during bottle feeding (p < 0.025), but weight gain during breast-feeding sessions was less (median, no gain vs 31 gm, p < 0.001). We conclude that (1) very low birth weight infants can tolerate both breast and bottle feedings at the same postnatal age; (2) very low birth weight infants are less likely to have oxygen desaturation to less than 90% during breast-feeding; and (3) weight gain is less during breast-feeding, probably because of lower intake, and may require more lactation counseling or supplementation of the feedings.