The composition and content of the gastric phospholipids were followed during development and healing of indomethacin-induced chronic, antral ulcers in rats. The individual phospholipids were identified by thin-layer chromatography and quantitatively estimated by spectrophotometric analysis of phosphate. No changes were found in phospholipid composition and content after a 24-hour fast or during the first 24 h after indomethacin was given. The total phospholipid content and the content of lysophosphatidylcholine and phosphatidylcholine were increased on the 5 th day, when chronic ulcers were established. After 4 weeks, when the ulcers were healed, the total phospholipid content, and content of phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol, respectively, were decreased, while the content of lysophosphatidylcholine was increased. In conclusion, the composition and content of gastric phospholipids were altered in rats with ulcers as well as in rats with healed ulcers.