Effects of KU-54 on the biosynthesis of glycoprotein in the gastric mucosa and the liver, as measured by the rate of incorporation of 14C-glucosamine, were investigated in rats under various conditions after a single administration of 14C-glucosamine of (9.88 microCi/animal, ip). 14C-glucosamine was incorporated with relative ease in the acid-insoluble fraction of the gastric mucosa. KU-54 at 100 mg/kg was orally administered twice daily for 5 days in rats (though it was given once on the 5th day) before injection of 14C-glucosamine. The rate of 14C-glucosamine incorporation into the acid-insoluble fraction of the gastric mucosa was significantly increased by KU-54, but that of the hepatic tissue was not increased. In addition, hydrocortisone (20 mg/kg) also produced a drop of incorporation of 14C-glucosamine in the gastric mucosa, but oral KU-54 at 100 mg/kg twice daily for 5 days (though it was given once on the 5th day) significantly inhibited the drop of incorporation of 14C-glucosamine in the gastric mucosa, but that in the hepatic tissue was not inhibited. Therefore, the effects of KU-54 were greater in the gastric mucosa than in the hepatic tissue. On the 5th day of the ulcer produced by acetic acid in rats, the specific radioactivity in the mucosa of the margin of the ulcer increased significantly compared with that in the normal (non-ulcerative) mucosa, but this phenomenon was not affected by KU-54.(ABSTRACT TRUNCATED AT 250 WORDS)