S U M M A R YForty-five patients taking long-term indomethacin and with endoscopic erosions or superficial ulcers in the oesophagus, stomach or duodenal bulb were randomized in a double-blind study to continue with standard indomethacin or receive a ' delayed-release' formulation. This consisted of microgranules of indomethacin coated with an acrylic resin, Eudragit L, which releases drug in the small intestine. Endoscopy was repeated after 8 weeks and biopsies taken on both occasions. Changes in endoscopic lesions and histological appearances were similar in both groups, although mucosal erythema was less in those given Eudragit L indomethacin. Systemic, rather than topical, effects of indomethacin may therefore be responsible for persistence of gastro-duodenal mucosal lesions in these patients. There is reason to question the clinical practice of using expensive, delayed-release preparations.