During the immediate postnatal period, the gastrointestinal (GI) tract undergoes profound growth, morphological changes and functional maturation. The oesophagus shows an accelerated cell proliferation in the epithelium and an increased production and accumulation of mucus in the glands. The stomach shows a rapid tissue growth and a marked increase in acid secretion capacity. The intestine shows increased tissue growth and marked epithelial modifications; the latter include the loss of the ability by the epithelial cells of the small intestine to absorb macromolecules, and the loss of the ability by the epithelial cells of the large intestine to synthesize digestive enzymes and to absorb amino acids and glucose. These changes are apparently related to the onset of colostrum ingestion, because starved or water-fed newborns showed little changes in the GI tract. A number of hormones and growth-promoting peptides, such as insulin, cortisol, epidermal growth factor (EGF) and insulin-like growth factor I (IGF-I), have been found at high concentrations in the maternal colostrum. There is evidence that colostrum-bone EGF and IGF-I play a role in postnatal GI development in newborns. The role of other colostrum-borne hormones and growth-promoting peptides remains to be assessed. Further studies are also required to demonstrate if colostrum-borne EGF and IGF-I can be used therapeutically to those newborns with immature or diseased GI tract, such as in cases of premature birth or prenatal growth retardation or cases requiring total parenteral nutrition.