OBJECTIVE The measurement of serum pepsinogens is clinically useful to represent gastric acid secretion. Since both serum pepsinogens and gastric acid secretion are considerably altered by H. pylori eradication, the correlation between these two parameters could be different prior to and after eradication. In this study, we investigated the correlation between the two parameters prior to and after eradication. METHODS One hundred eighteen H. pylori-positive patients with peptic ulcers or chronic gastritis were enrolled in this retrospective analysis. In all participants both the measurement of serum pepsinogens and the determination of gastric acid secretion were performed prior to and at 1 month after successful eradication. In 85 subjects, the same assessments were repeated at 7 months. Correlations between serum pepsinogens and gastric acid secretion were assessed using linear regression analysis. RESULTS The pepsinogen I/II ratio (r = 0.56) was a better indicator of gastric acid secretion in H. pylori-infected subjects than pepsinogen I itself (r = 0.31). Eradication of H. pylori altered the association, causing pepsinogen I (r = 0.55) to become a better indicator of gastric acid secretion compared with the pepsinogen I/II ratio (r = 0.40) at 1 month after eradication, followed by similar tendencies at 7 months. CONCLUSIONS Using different serum biomarkers (pepsinogen I/II ratio prior to eradication or pepsinogen I after eradication), the measurement of serum pepsinogens is useful for predicting the individual gastric acid secretion level not only in H. pylori-infected subjects, but also in subjects with histories of eradication of the infection.