Twenty-four-hour esophageal pH monitoring is currently the most sensitive test for diagnosing gastroesophageal reflux. Little is known, however, about the effect of aging and gender on esophageal acid exposure in asymptomatic individuals. Thirty asymptomatic volunteers underwent 24-hr esophageal pH monitoring. Fifteen were < 65 years (eight female, seven male) and 15 were > or = 65 years (seven female, eight male). In this asymptomatic group no significant difference was seen by age, while males were found to have significantly more esophageal acid exposure than females. The need for sex-specific normal 24-hr pH monitoring values is suggested. Thirty percent of these asymptomatic subjects were abnormal by conventional 24-pH criteria. The clinical importance of these "silent refluxers" is unknown.