The difference of inhibit ion mechanisms between secretin and gastrone on gastrin-stimulation was investigated from the view point of the change of carbonic anhydrase activity (CA), histamine content (Hm), histidine decarboxylase activity (HD) in gastric mucous membrane ; gastric mucin secretion, enzyme activity in parietal cell (histochemically on succinic dehydrogenase (SD) and CA and mitochondria activity (Mt) (phase contrast microscopically). The results obtained are as follows; 1) Both secretin (S) and gastrone (Go) inhibited the increase of CA due to gastrin-stimulation. 2) Although secretin did not show any effects on the decrease of H m and on the increase of HD due to gastrin stimulation, Go resulted in the increase of Hm and decrease of HD. 3) Both secretin and gastrone showed the same effect son gastric mucin secretion, SD, CA, and Mt on gastrin stimulation. From the above results, we noted that S and G are the same in the effects, but not in the mechanisms of inhibiton.