Gastric contents retained in rat stomach following mild irritant exposure contribute to adaptive cytoprotection. Fluid retained in the gastric lumen immediately preceding the administration of a damaging product will dilute that product and decrease its injurious capacity. In an attempt to explain the phenomenon of adaptive cytoprotection, we studied the effect of mild irritant exposure on the volume of fluid retained in the gastric lumen. Rats treated with 0.2 N-0.4 N HCl had a larger volume of gastric fluid retained as compared to animals treated with 0.4 N NaCl. Additionally, a mixture of gastric juice derived from rats exposed to 0.4 N HCl with 2 ml ethanol was significantly less damaging to the gastric mucosa than a similar mixture containing an equal volume of gastric juice derived from 0.4 N NaCl-exposed rats. We conclude from our observations that in mild irritant-exposed stomachs, the gastric juice is a main contributor to the protection against ethanol injury. 