Many patients, who suffer of heartburn or non ulcerous dyspepsia, seem to have a normal gastric mucosa (gastroscopy or histology). Potential difference is a measurement of the efficacity of mucosal barrier, and it drops when healthy volunteers ingest aspirin. By this method it is shown that patients with non ulcerous dyspepsia have a weakness of gastric mucosal barrier. Compare to controls or irritable bowel syndrome, basal potential difference is lower and time to return to basal value after aspirin is longer. This test shows that a trouble of the mucosal barrier exists even if the mucosa seems to be normal at gastroscopy and histology.