The high mortality associated with the surgical treatment of erosive gastritis is related to the postoperative continuing haemorrhage rate. Immediate gastroscopy has significantly improved preoperative diagnosis, and in 30 cases treated by the Billroth I operation continuing haemorrhage was seen on only one occasion.The frequent association of chronic gastritis and drug-associated erosive gastritis suggests that the gastritic mucosa is unusually susceptible to aspirin. Experiments designed to investigate the effect of biliary diversion on aspirin-induced gastric mucosal damage demonstrated a significant increase in such damage.Intestinal metaplasia and chronic gastritis of the gastric mucosa develop when upper intestinal secretions are diverted into the stomach either surgically or by pyloric regurgitation. Postoperative gastric aspiration indicates that the Billroth I operation is associated with far less regurgitation of upper intestinal secretions postoperatively than either the Polya operation or vagotomy and drainage. It is suggested that the efficacy of the Billroth I operation in controlling haemorrhage in the immediate postoperative period is related to this. In the long term the reduced incidence of intestinal metaplasia in the Billroth I gastric remnant reflects a minimal tendency to biliary reflux.