The gastrointestinal mucosa displays a number of different cell lineages in response to injury. The presence of such phenomena has been known for a number of years but their significance is only now being realised.1-3 A number of these are thought to be reparative mechanisms, such as the ulcer associated cell lineage (UACL) at the edge of small bowel ulcers (see fig 1).4 Other examples include spasmolytic polypeptide expressing metaplasia5 and pseudopyloric metaplasia in the stomach. Other metaplastic cell lineages, such as intestinal metaplasia in the stomach and the glandular metaplasia of Barrett's oesophagus, have a neoplastic potential but are also a response to an initial mucosal injury. In an animal model of duodenal content …