We report a study of 127 patients examined with esophago-gastroduodenoscopy and with a diagnosis of chronic gastritis (by biopsy), and gastric peptic ulcer and duodenal peptic ulcer (endoscopically). Brushing samples and biopsies were taken from the esophagus, stomach, and duodenum. Gram stains of brush-collected samples, culture of brush samples and biopsies were performed in order to detect the presence of PC. In cases of chronic active gastritis, PC was found in 91% of patients. It was found in 73% and 84%, respectively, of cases of gastric and duodenal ulcer. PC was found with equal frequency in the cardia and body as in the antrum of infected individuals, but no confirmed cases of colonization of the esophagus or duodenum were found. The most efficient methods for identifying PC colonization were (in descending order of efficiency), silver stain of biopsies, Gram stain of brushings, hematoxylin-eosin stain of biopsies, culture of biopsies, and culture of brushings. In some cases, we have identified PC in the esophagus and duodenum by gram stain and culture, but no not by silver stain or H&E stain of biopsies, suggesting that contamination from other areas of the stomach may be an occasional problem in sampling these areas for PC.