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The Air Flow Sphincter Locator (AFSL) is marketed as an alternative method to manometry for localizing the lower esophageal sphincter (LES) for pH probe placement. Such a system is desirable due to the additional time, cost, and discomfort associated with dual nasal intubation, but its accuracy has never been assessed. To assess the accuracy of the AFSL in localizing the LES. Fifty consecutive outpatients presenting for pH and manometry studies were included. The upper border of the LES was determined using HRM and the AFSL by two technicians independently. LES locations measured by technicians using AFSL versus manometry, as well as the manometrically determined LES locations by technicians versusMDs were compared. Differences in LES locations determined by HRM as read by MDs versus technicians were small; none were >3 cm, and 92% were within 2 cm. Comparison between LES locations determined by technicians using HRM versus the AFSL revealed that 52% had a difference of 2-3cm and 32% had a difference of >3 cm. Hiatal hernia was associated with a difference in LES location of >3 cm. Excluding patients with hiatal hernia, nonetheless, still produced a >3 cm difference in 24% of studies. Prior reports have suggested that a difference greater than +/-3 cm in pH probe placement is considered unacceptable for clinical studies. Based on our study, the AFSL placed the LES outside of this range in 32% of patients, and may be particularly inaccurate in the setting of a hiatal hernia. This suggests that the device may not be an acceptable alternative to manometry in determining LES location for pH probe placement. [ABSTRACT FROM AUTHOR]