The histologic demonstration of characteristic curved, spiral bacilli on the gastric mucosa is considered the gold standard for the diagnosis of Helicobacter pylori infection. However, in some cases the urea breath test or serologic tests may be positive, yet gastric biopsy specimens fail to reveal H. pylori. The objectives of this study were (1) to analyze the density and distribution of H. pylori in different regions of the stomach, (2) to ascertain which area of the stomach is a preferential site for obtaining biopsy specimens, and (3) to determine whether the presence of neutrophils or lymphoid aggregates correlates with the presence of detectable organisms in the same biopsy specimen. Eighty-nine patients with H. pylori infection underwent gastric mapping. The density of H. pylori, neutrophils, and lymphoid follicles was assessed semi-quantitatively in each biopsy site. The likelihood of getting a false-negative result was also calculated for each biopsy site. All biopsy specimens from the antral lesser curvature, at or near the incisura, had detectable H. pylori. Scores for this area and the cardia were higher than scores for the gastric corpus, but most differences were not significant. Fewer than 3% of antral biopsy specimens were false-negative, compared to between 6% and 9% of those from the corpus (p = 0.02). Neutrophils were present in more than 94% of all antral biopsy specimens, compared to 60% to 86% of specimens from the corpus (p < 0.01). Lymphoid follicles were detected in approximately two-thirds of antral biopsy specimens but in fewer than half of those from the corpus.(ABSTRACT TRUNCATED AT 250 WORDS)