Previous studies suggest that trypsin and bile salts are the causative agents in alkaline reflux esophagitis. However, their individual effects on the esophageal mucosa is relatively weak when used alone. Since these agents seem to have different sites of action in the esophageal mucosa, we have investigated whether they might have a synergic action when used in combination. Rabbit esophagus was perfused in situ with a test solution containing trypsin and cholate, alone or in combination, at pH 7.0. The severity of mucosal damage was assessed, using as indicators of mucosal integrity transmucosal potential difference, net flux of Na+, and mucosal permeability to two neutral molecules of different sizes, 3H-H2O and 14C-erythritol. Cholate (in its conjugated and deconjugated form) was chosen as the bile salt test agent, because it is quantitatively important but almost inert on the esophageal mucosa when used alone. The results indicate that trypsin significantly decreased potential difference and increased mucosal permeability to Na+, 3H-H2O and 14C-erythritol. Cholate and taurocholate had no influence on the mucosa when used alone, but cholate, especially in its deconjugated form, increased significantly mucosal damage caused by trypsin. The findings suggest that trypsin and bile salts do have a synergic effect on esophageal mucosa, which may have pathogenetic significance in clinical alkaline reflux esophagitis.