The incidence of sudden infant death syndrome has been found to be consistently higher in preterm and low birth weight infants than in infants born at term. Failure to arouse from sleep is one possible mechanism for sudden infant death syndrome. This study compared the arousal responses to nasal air-jet stimulation in a longitudinal study between groups of healthy preterm and term infants. Preterm infants (n = 9) were born at 31-35 wk gestation with normal birth weights for gestational age and studied on three occasions: a preterm study at 36 wk, at 2-3 wk post-term, and at 2-3 mo post-term. Term infants (n = 22) were born at 37-42 wk and were studied at 2-3 wk and 2-3 mo post-term. Arousal thresholds were determined in both active sleep (AS) and quiet sleep (QS). In preterm infants, there was no state-related difference in arousal thresholds at either the 36 wk or 2-3 wk study; however, at 2-3 mo, arousal threshold was significantly greater in QS than AS (p < 0.05). In contrast, in term infants, arousal thresholds were significantly elevated in QS compared with AS at both 2-3 wk and 2-3 mo (p < 0.001). Arousal thresholds in AS were not different between the two groups of infants, with both groups of infants remaining readily arousable. However, in QS at 2-3 mo, arousal thresholds were significantly lower in the preterm infants (p < 0.05). This study has demonstrated that arousability is altered by gestational and postnatal age. The lower arousability that characterizes QS in term infants regardless of age is not evident in preterm infants until 2-3 mo post-term age.