AbstractOesophageal biopsies from endoscopically normal patients were incubated in the following for up to 30 min—Ham's F10 medium:isotonic saline:0.1 N HCl:20, 2 and 0.2 mM bile acids:trypsin: pepsin:lipase; autologous gastric and duodenal juices. The biopsies were then examined by electron microscopy. No morphological change was produced by Ham's F10 or saline. HCl caused little damage. Gastric juice produced widespread severe damage, as did pepsin. Duodenal juice and the enzymes tested caused lysis and internalisation of desmosomes and peripheral cytoplasmic vacuolation. Bile acids split desmosomes and induced microvesiculation of the cell membranes. Similar microvesiculation was also induced by duodenal juice. All media except hydrochloric acid eventually produced organelle damage and leaky and disrupted cells. The functional and superficial cells appeared to be able to withstand attack from these experimental media better than did prickle and basal cells. Membrane coating granules were secreted in the presence of hydrochloric acid, but not with enzyme