['We hypothesized that changes in proximal and distal esophageal sphincter kinetics evoked upon pharyngeal provocation undergo longitudinal maturation.', 'Pharyngeal stimulation-induced reflexes were characterized using novel pharyngo-esophageal motility methods in 19 healthy premature neonates, studied at 34.7 ± 0.8 wk (time-1) and 39.3 ± 1.1 wk postmenstrual age (time-2). Graded volumes of air (290 infusions) and sterile water (172 infusions) were infused to define sensory-motor characteristics of upstream (pharyngeal reflexive swallow, PRS) and downstream (pharyngo-lower esophageal sphincter relaxation reflex, PLESRR) esophageal reflexes. Data displayed as mean ± SE.', 'Threshold volumes were similar with air and water for PRS and PLESRR at time-1 and time-2. Multiple PRS responses were noted with water stimulus and were different between the media (time-1 vs. air, P < 0.0001; time-2 vs. air, P = 0.0003). Dose-response relationships for water were significant (P < 0.01 for PRS and PLESRR time-1 and time-2), but not with air.'] Are upper and lower esophageal sphincter kinetics modified during maturation : effect of pharyngeal stimulus in premature infants?