Background: Helicobacter pylori is strongly associated with gastric and duodenal ulcer disease. However, the diagnosis of gastroduodenal ulcers requires an endoscopic or radiographic examination. In this study, we attempted to establish a relationship between the magnitude of [¹³C]urea breath test results or serum H. pylori IgG levels and endoscopic findings in H. pylori-infected individuals. Methods: Patients who had undergone endoscopy and had a positive [¹³C]urea breath test and/or positive H. pylori IgG serology were identified. Endoscopic diagnoses included duodenal ulcer, gastric ulcer, nonulcer dyspepsia, and others. Results of 6% or greater on the [¹³C]urea breath test was defined as positive for H. pylori infection. H. pylori IgG serology was determined by an enzyme linked immunosorbent assay with values of greater than or equal to 1.0 being seropositive. Results: One hundred seventy-five patients were seropositive (mean = 3.01 ± 1.58). One hundred sixty-eight patients had a positive [¹³C]urea breath test (mean = 25.43 ± 16.90). One hundred fifty-five patients were common to both the groups. Statistical analysis did not reveal any relationship between quantitative [¹³C]urea breath test results or H. pylori IgG values and endoscopic diagnoses. Conclusion: The magnitude of [¹³C]urea breath test or H. pylori IgG serology cannot be used to predict the presence or absence of gastroduodenal ulcer disease. (Gastrointest Endosc 1996;44:679-82.)