Serum immunoglobulin G (IgG) antibody tests are used extensively. We attempted to find out whether the titers of anti-Helicobacter pylori IgG antibody correlated with the degree of macroscopic gastrointestinal damage, the severity of antral gastritis, and the density of antral H. pylori colonization in symptomatic patients. Peripyloric antral biopsy specimens were obtained from 50 consecutive patients with dyspepsia undergoing upper gastrointestinal endoscopy. The macroscopic gastrointestinal damage and the histologic grades of antral gastritis were scored by a modified Lanza scale and Sydney system, respectively. In addition, the densities of antral H. pylori colonization were graded semiquantitatively. Serum IgG antibodies to H. pylori were measured by enzyme-linked immunosorbent assay. Thirty-six (M/F = 29/7) of the 50 patients had H. pylori infection documented by histologic examination or rapid urease test or both. Among the subjects, the IgG antibody titers to H. pylori correlated significantly with the grades of antral polymorphonuclear cell infiltration (p = 0.002) and antral bacterial density (p = 0.01) but not with endoscopic scores, the grades of mononuclear cell infiltration, mucosal atrophy, or intestinal metaplasia (p > 0.05). In addition, endoscopic scores also were found to be significantly correlated with antral bacterial density (p = 0.049) and the grade of polymorphonuclear cell infiltration (p = 0.012). We therefore conclude that high titers of IgG antibody to H. pylori in patients with dyspepsia indicate dense H. pylori colonization and severe antral polymorphonuclear cell infiltration. However, it cannot replace endoscopic examination to evaluate the degree of macroscopic gastrointestinal damage.