The carrier state was developed in 12 of 13 dogs given orally with 39-92 cells of S. typhimurium harbored in the canine feces, while none of 3 dogs with 60 cells of a fresh isolate of the serovar produced shedder state and antibody. In the former, the organisms were excreted in the feces for 18 to 24 days. The organisms settled in the mucosa of middle part of the ileum one day post-administration, and then, spread to the mucosae of lower part of the ileum, caecum, and upper part of the colon 2 or 3 days, giving the highest number in the ileal mucosa. On days 5 to 15, the multiplication of the organisms in the mucosae of those parts became prominent, especially in the parts adjacent to the ostium ileocaecocolicum. The jejunal lymph node became positive for Salmonella from the 2nd day. The antibody was found from the 7th day. None of the dogs showed clinical signs and gross lesions. Thus, it was demonstrated that the carrier state in dogs was the latent infection, and the ileal mucosa in the earlier stage of infection and the mucosae of neighboring parts to the ostium ileocaecocolicum in the later stage served as the major site of localization and multiplication. The infectivity of "the organisms in feces" to produce the carrier state was markedly higher than that of the fresh isolate.