Pouchitis is a well recognized entity but its aetiology is still controversial. The aim of this study is to determine if gastric acidity has a role in the physiopathology of this problem. In a series of 70 consecutive patients with pelvic reservoir (65 mucosal ulcerative colitis (UC), 5 familial adenomatous polyposis (FAP], 15 patients developed pouchitis. Ten patients responded favourably to metronidazole. Five patients had several episodes of resistant pouchitis. Two of these (with FAP) developed recurrent bouts of pouchitis while on cimetidine therapy for severe peptic disease. Both patients were improved on sucralfate and symptoms did not recur after highly selective vagotomy. The other three patients began to complain of pouchitis one to six years after the fabrication of the reservoir. Gastric studies were undertaken to determine the fasting gastric pH. The values were high in all three cases despite normal stimulation tests and normal gastric biopsy. After pouch removal for toxic dilatation (without obstruction) in one of these patients, the gastric pH returned to normal. From these preliminary results, it seems that pouchitis might be associated with hypochlorhydria. It might also be possible that certain physiologic properties of the reservoir reduce gastric acidity and so create recurrent bouts of pouchitis. Further studies are needed to evaluate the physiologic consequences of the pelvic ileal reservoir on gastric physiology.