We compared the prevalence of gastric metaplasia of the duodenal mucosa (GM) and its characteristics in 204 Peruvian patients from a low socioeconomic level with the corresponding prevalence reported in dyspeptic patients from a developed country, the United Kingdom. Gastric metaplasia was significantly less prevalent in the Peruvian than in the United Kingdom series. However, when present, GM was not significantly different in extent or frequency of colonization by Helicobacter pylori or association with active duodenitis, despite a higher prevalence of H. pylori-associated gastritis. Hypochlorhydria was markedly more frequent in the Peruvian than in the United Kingdom series. The finding of a low prevalence of H. pylori-colonized GM in patients with previously reported low prevalence of duodenal ulcer gives further support to a pathogenic link between both conditions. © 1992 Raven Press, Ltd., New York.