Reflux of bile into the stomach is common after surgery for duodenal ulcer disease; however, only a minority of patients may develop significant gastritis and pain. Gastric aspirates from two groups of patients after operation for duodenal ulcer were quantitatively and qualitatively analyzed. Group A patients were asymptomatic and the bile composition was normal. Group B patients were symptomatic and had a significant increase in the secondary bile acid, deoxycholic acid. The concentration of bile acid was similar in the two groups. This alteration in bile acid composition, with an increase in deoxycholic acid, may be an important factor in determining which patients with bile reflux develop gastritis.