We examined the difference between the normal microflora in the pharynx and the levels of serum immunoglobulins of the Expedition members during their stay in Japan and at Syowa and Mizuho Stations, Antarctica. 1) There was no evidence that the bacterial species and the number of microflora in the pharynx had changed during the first three months at Syowa Station. 2) The number of pathogenic bacteria in the pharynx increased in the middle of winter (June and July) at Syowa Station. 3) In midsummer (November and December) of Antarctica, the pathogenic bacteria in the pharynx increased, probably due to the outdoor work. 4) The pathogenic bacteria were not detected in the pharynx of the members living at Mizuho Station, the nearest station to the South Pole, where the mercury falls to about 30 to 40 degrees below zero for eight months. 5) No remarkable differences were recognized in the levels of IgG and IgM in serum of the members during their stay in Japan and in Antarctica. On the other hand, IgA of them showed a slight increase, which may be explained by enhanced activity of local immunity.