Twelve partially gastrectomized subjects who have consecutively undergone total biliary diversion for severe bilious vomiting were studied before and after operation in order to assess the effects of surgery on gastric histology and enterogastric reflux. Before and six months after operation, the following protocol was performed: (1) blood examinations including serum basal gastrin; (2) endoscopy with multiple gastric biopsies; and (3) quantitation of bile acids in the gastric aspirate. Of the preoperative symptoms, bilious vomiting and heartburn completely disappeared postoperatively in all the subjects. Fasting bile reflux was significantly reduced (bile reflux was annulled in six and considerably lowered in the remaining six subjects), and erythema of the gastric mucosa completely disappeared in all the subjects after diversion. Among histological findings, while a significant regression of foveolar hyperplasia was found both in the perianastomotic area and in the body of gastric remnant, none of the other aspects identifiable in postgastrectomy gastric mucosa (chronic gastritis changes included) were affected by diversion. These results show that biliary diversion is effective in correcting reflux, bilious vomiting, erythema, and foveolar hyperplasia of the gastric mucosa and confirm the suggested relationship between bile reflux and gastric foveolar hyperplasia.