Gastroesophageal reflux disease (GERD) is caused by esophageal exposure to concentrated acid over time. The authors tested the hypothesis that AUC for hydrogen ion activity (H/sup +/) modeled by the power function, predicts mucosal damage and propose that GERD is a two component disease. In 33 continuous 24-h esophageal pH recordings (Hines VA Hospital) the AUC H/sup +/ was calculated and correlated with Savary-Miller grades of esophagitis. A functional relationship between the relative importance of AUC H/sup +/ and H/sup +/ was derived using the power function with two parameters (/spl beta//sub 1/ and /spl beta//sub 2/). The mean values of AUC H/sup +/ activity by endoscopic grade were significantly different (p<0.001, Kruskal-Wallis test). The lowest mean value corresponded to grade 1 and the highest to grade 4. The power function plot of each endoscopy grade shows two different patterns at low and high values of H/sup +/.