BACKGROUND Trefoil factor 1 (TFF1/pS2) is a major secretory product of the stomach and TFF1 knockout mice constantly develop adenomas and occasional carcinomas in the pyloric antrum. AIM To analyse the role of TFF1 in the differentiation of gastric epithelial cell lineages using oxyntic mucosae from normal and TFF1 knockout mice. METHODS The various cell lineages were labelled using specific markers of pit, neck, parietal, and enteroendocrine cells. Patterns of TFF1, TFF2, and TFF3 expressions were defined using western blotting, immunohistochemistry, and/or immunogold electron microscopy. RESULTS In normal mice, starting from postnatal day 1 (P1), TFF1 and TFF2 were produced by mucus secreting cells of the developing epithelium. At P7, TFF3 expression occurred in pit and parietal cells. When oxyntic glands were compartmentalised, at P21 and in older mice, TFF1 and TFF2 were expressed in pit and neck cells, respectively, and TFF3 was no longer in parietal cells but became a feature of zymogenic cells. In TFF1 deficient mice, alteration of oxyntic epithelial differentiation became obvious at P21, showing significant amplification of pit cells at the expense of parietal cells. At the molecular level, lack of TFF1 induced dramatic inhibition of TFF2 expression and more precocious TFF3 expression. CONCLUSION In the oxyntic mucosa, all three TFFs are produced in a lineage specific manner and TFF1 is essential in maintaining the normal commitment programme of epithelial progenitors.