Objectives: To characterize esophageal body and lower esophageal sphincter (LES) motor function in very premature infants. Study design: Esophageal manometry was performed in 12 very premature infants of 26 to 33 weeks’ postmenstrual age (PMA) (body weights of 610-1360 g). Esophageal motor patterns were recorded for 30 minutes with a perfused micromanometric sleeve assembly (outer diameter, 2.0 mm). Results: Esophageal pressure waves triggered by dry swallows were predominantly (84%) peristaltic in propagation sequence. All infants showed tonic LES contraction; the mean resting LES pressure (LESP) for individual infants ranged from 5.0 ± 4.1 mm Hg to 20.0 ± 4.8 mm Hg. In all infants the LES relaxed (duration, 5.8 ± 3.0 seconds; nadir pressure, 1.8 ± 2.6 mm Hg) in response to pharyngeal swallows. Transient LES relaxations (TLESRs) (duration, 21.7 ± 8.7 seconds; nadir pressure, 0.1 ± 1.8 mm Hg) occurred on average 2.6 ± 1.6 times per study; 86% of these relaxations triggered esophageal body common cavity events known to be associated with gastroesophageal reflux. Conclusions: Esophageal motor function is well developed in very premature infants. Our data also suggest that TLESR is the predominant mechanism of reflux in these babies. (J Pediatr 1999;135:517-21)