Gastric emptying of meals of human milk and infant formula was studied in 11 healthy preterm (AGA) infants using a marker dilution technique. Gastric emptying rate and gastric half-emptying time were compared with data from 17 healthy infants aged 4 weeks to 6 months. The amounts of human milk emptied from the stomach per 0.1 m2 of body surface area were 19.4 +/- 4.5 ml in preterm infants and 29.5 +/- 4.6 ml in term infants. The corresponding amounts with meals of infant formula were 13.8 +/- 2.8 and 22.7 +/- 4.2 ml, respectively. With the volumes given gastric half-emptying times for meals of human milk and infant formula were 25.1 +/- 11.5 and 51.9 +/- 9.8 min, respectively, in preterm infants. The corresponding half-emptying times for term infants were 48 +/- 15 and 78 +/- 14 min, respectively. The differences in gastric emptying rate as well as in gastric half-emptying time between the two meals were significant (p less than 0.01) both in preterm and term infants.