Objective: To investigate the threshold amount of constantly infused feed needed to trigger lower esophageal sphincter relaxation (TLESR) in the right lateral position (RLP) and left lateral position (LLP). Study design: Eight healthy infants (3 male; gestational age: 32.9 ± 2.4 weeks; corrected age: 36.1 ± 1.3 weeks) were studied using an esophageal impedance-manometry catheter incorporating an intragastric infusion port. After tube placement, infants were randomly positioned in RLP or LLP. They were then tube-fed their normal feed (62.5 [40 to 75] mL) at an infusion rate of 160 mL/h. Recordings were made during the feed and 15 minutes thereafter. The study was repeated with the infant in the opposite position. Results: More TLESRs were triggered in the RLP compared with LLP (4.0 [3.0 to 6.0] vs 2.5 [1.0 to 3.0], P = .027). First TLESR occurred at a significantly lower infused volume in RLP compared with LLP (10.6 ± 9.4 vs 21.0 ± 4.9 mL, P = .006). The percentage of feed infused at time of first TLESR was significantly lower in RLP compared with LLP (17.6% ± 15.5% vs 35.4% ± 8.02%, P = .005). Conclusions: In the RLP, TLESRs and gastroesophageal reflux are triggered at volumes unlikely to induce gastric distension.