It has been postulated that reflux of bile into the stomach promotes gastric carcinogenesis. Bile-stained aspirates from 50 asymptomatic patients, partially gastrectomized more than 10 years earlier, were examined bacteriologically and with regard to conjugated and deconjugated bile acids. Endoscopic biopsies showed atrophic gastritis in all patients, cancer in two and severe dysplasia in another two. pH in the reflux aspirates was 7.3 +/- 0.4 (mean +/- standard deviation). Bacterial cultures were positive in all patients studied. Fecal type flora, mostly E. coli, klebsiella and Clostridium perfringens, was found in 85% of the patients. Total bile acids were found to be 2.6 +/- 2.0 mg/ml, 23% of which were deconjugated. Deoxycholic acid, known to promote carcinogenesis in animals, amounted to 27% of total bile acids and deconjugated deoxycholic acid was 5% of total bile acids. The mostly anaerobic microflora and the presence of mainly free secondary and primary bile acids may contribute to the high incidence of cancer in the gastric remnant observed after Billroth I or II operations.