Low-compliance perfusion manometry and clinical outcome were used to assess the chronic effects of feeding on functional maturation of the preterm intestine in 32 infants. During the first postnatal week, 16 infants received a small volume of formula to supplement their routine parenteral nutrition (24 ml.kg-1.day-1), and 16 received an equal volume of water. After 10 days of enteral "feedings," the manometric tracings of those infants who had received nutrient feedings had more migrating activity (P < 0.01) and less clustered phasic activity (P < 0.05) during fasting than did the tracings of those infants who had received nonnutrient feedings containing sterile water. Infants who received nutrient feedings demonstrated a change in motor activity in response to feeding; infants who had received water feedings failed to show a change in motor activity in response to feeding. After water-fed infants were given formula feedings for 2 wk, their motor activity patterns were similar to those who had initially been fed formula, and their motor responses to feeding were restored. Despite normalization of their motor activity patterns by 1 mo of age, these water-fed infants established full enteral nutrition and full nipple feedings later than did infants who had been fed formula (P < 0.01), suggesting that the delay of enteral feedings in preterm infants does not permit optimal intestinal maturation of nonmucosal functions.