Helicobacter pylori (H. pylori) eradication increases the serum pepsinogen (PG) I/PG II ratio and the percentage change in PG I/PG II ratios was found to be a useful marker of H. pylori eradication (e.g., the PG method). We studied whether the PG method could be an early diagnostic marker of H. pylori eradication even in patients persistently treated with a proton pump inhibitor. Sixty-two H. pylori-positive patients underwent H.

pylori-eradication therapy, followed by treatment with a PPI to cure ulcers. Serum levels of PG I and PG II were measured before, at the end of, and at 4 weeks after the eradication therapy. At more than one month after the end of treatments, 13C-urea breath test (UBT) was performed. The cut-off values of percentage changes in PG I/PG II ratios for the diagnosis of eradication of H. pylori were set in proportion to PG I/PG II ratios before eradication in accordance with our previous report. Using the results of UBT as the standard, the percentage change in serum PG I/PG II ratios is useful as an early diagnostic marker for judgment of H. pylori eradication irrespective of PPI treatment.