Gastric biopsy specimens from patients who have undergone gastric surgery frequently exhibit foveolar hyperplasia, oedema, vasodilatation and congestion, and a paucity of inflammatory cells as consequences of entero-gastric reflux. Similar, albeit generally milder, changes were found in 47 of 316 (15%) non-surgical patients undergoing endoscopy for dyspeptic symptoms. To relate these changes to bile reflux or other potential gastric irritants the total bile acid concentration was measured in samples of fasting gastric juice, and the use of a symptom questionnaire ascertained the patients' cigarette consumption, use of non-steroidal anti-inflammatory drugs (NSAIDs), and alcohol intake. When patients with reflux gastritis were compared with normal controls (n = 91), significant increases in associated peptic ulceration and NSAID use were found in the group with reflux, but no increases in bile acid concentrations. Indeed, only one patient had evidence of duodenogastric reflux. It is concluded that most cases of "reflux gastritis" in the intact stomach are not due to reflux of bile. Our findings indicate an important pathogenic role for long term NSAID use, in what might be usefully termed type C or "chemical" gastritis.