In adults, migrating motor complexes (MMCs) appear to be partially under hormonal modulation by motilin and pancreatic polypeptide. Preterm infants do not exhibit MMCs until 32 wk of gestation. Although plasma concentrations of motilin are similar in infants and adults, it is not known if actual hormonal modulation of MMCs is present in infants. In the first study we assessed whether plasma concentrations of motilin and pancreatic polypeptide surge with the occurrence of MMCs in term infants. In the second study we assessed whether erythromycin, a motilin receptor agonist, could induce migrating motor activity in preterm and term infants. In the first study we recorded motor activity in nine term infants who had never been fed. We determined plasma concentrations of motilin and pancreatic polypeptide in the presence and absence of MMCs. In the second study we gave the motilin agonist erythromycin intragastrically to 21 infants at a range of 24-42 wk of gestation to assess whether migrating activity could be induced via the motilin receptor. In the first study, plasma concentrations of motilin were similar during the presence and absence of MMCs, as were plasma concentrations of pancreatic polypeptide. In the second study, the administration of erythromycin induced the appearance of migrating activity in 7 of 14 infants who were older than 32 wk but in none of the infants who was younger than 32 wk. Although the motilin receptor appears to be functionally present beyond 32 wk of gestation, as assessed by in indirect pharmacologic challenge, hormonal modulation of migrating activity in the neonate by plasma motilin and pancreatic polypeptide is absent.