Retinoic acid (RA) is a powerful differentiation agent. Barrett's oesophagus occurs when duodeno-gastro-oesophageal reflux causes squamous epithelium (SE) tissue to become columnar epithelium tissue by an unknown mechanism. The bile acid lithocholic acid (LCA) competes for the retinoid X receptor retinoid binding site. Hence, RA pathways may be implicated in Barrett's oesophagus.