Respiratory sinus arrhythmia (RSA), a non-invasive indicator of vagal regulation of the heart, and heart period (HP) were monitored before, during, and after oral or gastric-tube bolus feedings in 32 preterm infants. Group 1 infants (n=15) were ≤30 weeks gestational age (GA) at birth (mean 28.3 weeks) and group 2 infants (n=17) were ≥31 weeks GA at birth (mean=33.2 weeks). Mean postmenstrual ages at the time of study were 33.5 ± 2.3 (SD) weeks in group 1 and 33.9 ± 1.6 (SD) weeks in group 2. RSA and HP decreased in both groups during feeding. However, postfeeding RSA and HP increased toward prefeed levels only for group 2 infants. In addition, RSA and HP changes during feeding were correlated only for group 2 infants. The results suggest that the preterm infant may experience a maturational lag in vagal function and in the influence of vagal activity on metabolic mechanisms (i.e. heart rate) related to ingestive needs. This maturational lag may contribute to continued feeding difficulties and may be a measurable marker of subtle neurodevelopmental problems.