The morphology of the esophageal mucosal damage induced by lysolecithin was investigated in an experimental model, where an isolated segment of rabbit esophagus was purfused in situ with lysolecithin, alone or in combination with HCl. The results indicate that lysolecithin alone causes no morphological damage to the esophageal mucosa. However, when combined with HCl, lysolecithin causes widening of intercellular spaces and detachment of superficial cells leading ultimately to disclosure of denuded submucosal collagen bundles. This suggests that, in clinical situations lysolecithin refluxed from the duodenum into the stomach and further to esophagus may have importance in the pathogenesis of reflux esophagitis when gastric acid is present, too. In contrast, under unacidic conditions (i.e., in the pathogenesis of alkaline reflux esophagitis) lysolecithin seems to be of minor importance.