Detailed analyses of biochemical and microbiological variables such as pH, nitrite concentration, total viable counts (TVC), nitrate reductase-positive bacterial counts (NRPBC), and identification of microorganisms were carried out on 76 fasting gastric juice samples obtained at endoscopy from 64 patients previously submitted to partial gastrectomy (22 end-to-end Billroth I, 42 Billroth II/Reichel-Polya) and from 12 normal controls. Samples from normal controls were sterile, but bacteria were detected in the juice from all the operated patients. Significantly higher mean pH values and nitrite levels (p less than 0.001) were found in partial gastrectomies than in normal controls. In relation to surgical methods, higher mean pH values (p less than 0.005), nitrite levels (p less than 0.01), TVC (p less than 0.01), and NRPBC (p less than 0.005) were observed in the juice of patients with Billroth II as compared with Billroth I gastrectomies. Anaerobic bacteria, typical of faecal flora, and particularly Escherichia coli (p less than 0.05) characterized Billroth II samples. All these data suggest that the presence of bacteria in the gastric juice of gastroresected patients can be considered a risk factor of gastric neoplasia and that the type of operation used for the reconstruction of digestive continuity may influence the magnitude of this risk.