BACKGROUND: The mechanism against entry of gastric content into the pharynx during high intensity vocalization such as seen among professional singers is not known. We hypothesized that phonation induces UES contraction enhances the pressure barrier against entry of gastro-esophageal contents into pharynx. AIMS: To determine and compare the effect of phonation on luminal pressures of the esophagus and its sphincters. METHODS: We studied 17 healthy volunteers (7M, 10F) by concurrent high resolution manometry and voice analysis. We tested high and low pitch vowels sounds. Findings were verified in 6 subjects by UES manometry using a water perfused sleeve device. 8 of 17 volunteers (2M, 6F) had concurrent video fluoroscopy with high resolution manometry and voice recording. Fluoroscopic images were analyzed for laryngeal movement. To define the gender effect, subgroup analysis was performed. RESULTS: All tested phonation frequencies and intensities induced a significant increase in UES pressure (UESP) compared to pre-phonation pressure. The magnitude of UESP increase was significantly higher than that of the distal esophagus, the LES and the stomach. Concurrent videofluoroscopy did not show posterior laryngeal movement during phonation eliminating a purely mechanical cause for phonation induced UESP increase. Sub-group analysis demonstrated phonation induced UESP increases in males were significantly greater than those of females. CONCLUSIONS: Phonation induces a significant increase in UESP suggesting the existence of a phonation-induced UES contractile reflex. UESP increase due to this reflex is significantly higher than that of the distal esophagus, LES and stomach. The phonation-induced UESP increase is influenced by gender.