OBJECTIVE To examined the changes in basal plasma concentrations of glicentin in developing children and the postnatal and postprandial changes in plasma glicentin levels in infants. METHODS Glicentin, an active component of enteroglucagon, is considered to have a significant trophic action on the intestinal mucosa. Fasting plasma concentrations of glicentin in healthy children and in term and preterm infants were measured before and 30 min after feeding during the first 14 d of life. RESULTS Plasma basal concentrations of glicentin in children under 1 y of age were significantly higher than those in children aged 1 to 15 y. Plasma basal concentrations of glicentin at 5 or 6 d (2496 and 2190 pg/ml) and at 14 d (2987 and 2817 pg/ml) after birth were significantly higher than those at 1 or 2 d (1098 and 1240 pg/ml) after birth in normal birthweight (NBW) and low-birthweight (LBW) infants. There was no significant difference in the glicentin level between infants at 1 or 2 d (1864 pg/ml) and at 5 or 6 d (1910 pg/ml) after birth in very-low birthweight (VLBW) infants, but the levels at 14 d (3310 pg/ml) after birth were significantly higher than either of those levels. Plasma glicentin concentrations after feeding were significantly higher than those before feeding at 1 or 2 d and at 5 or 6 d after birth in NBW and LBW infants, but a significant increase in the plasma glicentin level after feeding was first observed at 14 d after birth in VLBW infants. There were no significant differences in the basal plasma (2401 and 2718 pg/ml) and postprandial (3007 and 3912 pg/ml) glicentin levels between breastfed and formula-fed infants. CONCLUSIONS The results of the study suggest that glicentin may play an important role in intestinal mucosal growth in the early period of life, although its role in VLBW infants should be further investigated.