The incidence and relationship of intestinal metaplasia of the gastric antrum and gastric metaplasia of the first part of the duodenum were studied in endoscopic biopsies from 120 patients with nonulcer dyspepsia. Intestinal metaplasia was present in 29% of antral biopsies and gastric metaplasia in 39% of duodenal biopsies, with 9% of patients having both. Intestinal metaplasia was not related to alcohol consumption, but was significantly higher in patients who smoked 10 cigarettes or more daily. (P less than 0.002). Gastric metaplasia was associated with duodenitis. Its incidence was significantly higher in males (P less than 0.001) and in patients with a history of high/moderate alcohol intake (P less than 0.02); these findings are reminiscent of the presence of a similar relationship between these factors and duodenal ulcers and support the suggestion that duodenitis and duodenal ulcers probably represent different parts of a single disease spectrum. The presence of both types of metaplasia in 9% of the patients suggest that factors other than gastric acidity may influence the development of metaplasia.