BACKGROUND Twenty four hour esophageal pH monitoring is considered the gold standard investigation for gastroesophageal reflux disease. This test allows the linkage of symptoms to occurrence of reflux episodes and is used to record the frequency of reflux and the amount of esophageal acid exposure that results from reflux. AIM To know the acid esophageal exposure in healthy Chilean subjects. SUBJECTS AND METHODS Thirty two asymptomatic volunteers aged 30 to 76 years old (24 female) underwent 24 h esophageal pH monitoring with a digitrapper Mark II Gold (Synectics Medical Stockholm). Total reflux episodes, episodes greater than 5 min, the longest reflux episode, the lapse with pH < 5, the percentage of time with pH < 4 and the score suggested by Johnson and De Mester were analyzed. RESULTS There was a mean of 20.9 reflux episodes per subject and 0.1 episodes of more than 5 min. The longest episode lasted 8 min and the mean total time of acid reflux was 10 min/24 h. Total percentage pH below 4 was 0.7% and the mean score was 3.2. No subject reported symptoms during the test. CONCLUSIONS For practical purposes, the upper limit of normal acid exposure in Chilean subjects is 2.4%.