In order to clarify the etiology of acute gastric mucosal lesions, we studied gastric mucosal UDP-galactosyl transferase (UDP-Gal-T) activity as a marker of the biosynthesis of gastric mucous in rats with brain injury induced by injection of α-cyanoacrylate. Twenty-four hours after the injection, 82% of the rats showed gastric mucosal redness or erosion, and output of acid and pepsin of these rats was lower than in the control rats. Serial analysis of UDP-Gal-T activity revealed that the enzyme activity of the rats with brain injury became lower 24 hours after the injection than in the control rats. Simultaneous injection of atropine sulfate inhibited the decrease in UDP-Gal-T activity. However, the decrease in the enzyme activity was not induced by restraint and water immersion of rats which is also known to induce acute gastric mucosal lesions. These results suggest that in the rat with brain injury the reduction of gastric mucous production plays an important role in the pathogenesis of the acute gastric lesion.