Cytotoxic activities of P.C.A. to normal parietal cells were demonstrated in vitro. The changes were very similar to those of thyroid cells provoked by Hashimoto serum. The cytotoxic component was found to be immunoglobulin G. Complement was not added. Rabbit anti-rat gastric mucosa sera had no effects on the gastric secretion in rats, but histochemical changes were demonstrated. The changes were transient and returned to the normal state 60 minutes after injection of Anti-RGM sera. Activities of succinic dehydrogenase were most affected, particularly 3 minutes after injection. Decrease of activities gradually recovered to the normal condition. The comparison of C.A.G. with C.Th. was made. By the comparison between C.A.G. and C.Th., and by the results of experiments, the author considers that C.A.G. has the immunologically identical aspects with C.Th.. The author also considers that some immunological mechanisma are playing a role in the pathogenesis of C.A.G.