1.   The duodenal mucosa is normally challenged by intermittent exposure to acid, because of the periodic emptying of the gastric content into the duodenal lumen.

2.   In the first series of experiments, acid was administered into the duodenal lumen after pretreatment with saline to test the resistance to acid applied directly to the mucosa.

3.   The second lumen opened just beyond the pylorus and was used for pulse instillations of normal saline or acid into the duodenal lumen.

4.   Duodenal damage scores were plotted against the dose of acid instilled into the duodenal lumen.

5.   However, our experiments were performed after an overnight fast, and influences derived from the presence of traces of food within the duodenal lumen can be excluded.