Duodenal bulb biopsy specimens from 85 patients with non-ulcer dyspepsia (30 of whom had normal stomachs and 52 of whom had Campylobacter pylori gastritis) were examined for the presence and amount of gastric surface epithelial metaplasia (using both the hematoxylin and eosin stain and the Alcian blue-periodic acid-Schiff method), acute inflammation, and C. pylori (using the Giemsa stain). Gastric metaplasia occurred in the duodenal bulb in 61% of patients with gastric C. pylori and in an identical percentage for those who lacked C. pylori gastritis. For patients with gastric metaplasia, foci of metaplastic cells were seen in 70% of their bulb biopsy fragments. The Alcian blue-periodic acid-Schiff stain was superior to the hematoxylin and eosin stain for detecting gastric metaplasia. Only one of 33 patients without gastric C. pylori had gastritis and duodenitis. Fourteen of 52 (27%) patients with C. pylori gastritis had duodenitis; C. pylori was seen in the duodenal biopsy specimens from 13 of these patients. The organisms were often few, requiring oil immersion microscopy for detection. Each patient with duodenitis had gastric metaplasia, but some of these metaplastic foci were not inflamed. When present in the duodenum of patients with C. pylori gastritis, gastric metaplasia, acute inflammation, and C. pylori are typically patchy. Hence, several biopsy fragments of the duodenal bulb would be required for studies designed to determine the effectiveness of compounds used to treat C. pylori duodenitis.