In this prospective study 244 consecutive patients presenting with typical and chronic signs of gastroesophageal reflux were included. Conventional 24-hr esophageal pH monitoring was carried out to establish the symptom association probability, the concordance index, and the symptom sensitivity index. The symptom association probability could be calculated in 110 patients (45%). Two groups were identified: group 1 had normal duration of esophageal acid exposure; subgroup la (nonsignificant symptom association probability) included 39 patients (35.5%) and subgroup lb (significant symptom association probability) included 24 patients (21.8%); group 2 had abnormal duration of esophageal acid exposure; subgroup 2a (nonsignificant symptom association probability) included 21 patients (19.1%) and subgroup 2b (significant symptom association probability) included 26 patients (23.6%). In all, 56.6% of the patients presented typical symptoms of reflux not directly determined by one or repeated acid reflux episodes. The correlation between symptom association probability and the symptom sensitivity index allows for more accurate determination of esophageal acid sensitivity (subgroups lb and 2b).