Ambulatory 24-hour esophageal pH measurement is the standard for detecting abnormal esophageal acid exposure (AEAE), but it has a false negative rate of 15% to 30%. Wireless 48-hour pH monitoring (Bravo; Medtronic, Shoreview, MN) may allow more accurate detection of AEAE versus 24-hour pH monitoring. Forty-eight-hour wireless data were reviewed from 209 patients at three different tertiary care referral centers between 2003 and 2005. Manometric or endoscopic determination of the lower esophageal sphincter helped place the Bravo probe 5 to 6 cm above the lower esophageal sphincter. A total of 190 studies in 186 patients had sufficiently accurate data. There were 114 women and 72 men with an average age of 51 years. AEAE was defined by a Johnson-DeMeester score greater than 14.7 and was obtained in 115 of 190 studies (61%). Only 64 of 115 patients (56%) demonstrated AEAE for both days of the study, whereas 51 of 115 patients (44%) demonstrated AEAE in a single 24-hour period. There was no difference in the prevalence of AEAE on day 1 versus day 2 only (26% vs. 18%, P = .26). Compared with 24-hour alone data, 48-hour data showed 22% more patients with AEAE. Frequent day-to-day variability in patients with AEAE may be missed by a single 24-hour pH test. Forty-eight-hour pH testing may increase detection accuracy and sensitivity for AEAE by as much as 22%.