The pathogenetic effect of duodenogastric reflux of the development of gastric stump carcinoma was studied experimentally. In this animal model, 95 male Wistar rats were subjected to a specially designed gastrojejunostomy to divert the duodenal contents into the resected stomach through the afferent and efferent loop. The rats were fed normally without any carcinogen administration. The incidence of adenocarcinomas around the anastomosis of afferent loop was 0% at 10 weeks, 18.8% at 20 weeks and 34.4% at 40 weeks, so the incidence was apt to rise in parallel with passing of the weeks. At 40 weeks, the rats had a significantly higher incidence of adenocarcinoma in the gastric mucosa around the afferent loop than around the efferent loop (P < 0.05). Of particular interest is that invasive growth of the cancerous tissue into the liver was observed in one animal. Polypoid lesions called 'atypical hyperplasia' in the present study were similar to gastritis cystica polyposa of humans. The development of adenocarcinoma was found to be intimately connected with atypical hyperplasia, which might be promoted by repeated destruction and regeneration by duodenogastric reflux. These results suggest that the direct contact of the duodenal juice with the gastric mucosa induces carcinoma in the anastomotic lesion. From the clinical perspective, our findings suggest that a surgical technique that minimizes the duodenogastric reflux should be chosen.