Urinary epidermal growth factor (EGF) levels from infants receiving breast milk, a rich source of the growth factor, were compared with the levels excreted by infants receiving bovine milk based formulae or total parenteral nutrition that contains very little EGF. Although at 5-10 days after birth there was no significant difference in the urinary EGF output by the three groups of infants, by 13-17 days the urinary EGF output by breastfed infants was higher than by infants fed the two EGF-poor diets. These latter results are consistent with the hypothesis that EGF crosses the gastrointestinal wall to enter the general circulation in the suckling infant.