In three years, Corynebacterium diphtheriae was isolated from 1238 people, consisting of 820 North American Indians or Metis, 318 people of Caucasian origin, 97 Eskimos and 3 Asiatic Indians. Diphtheria infection of the throat, nose, ears and skin was common in the North American Indian and Metis people, but rarely caused severe symptoms. The infection occurred less often in white people but was more serious; of 27 cases of toxic respiratory diphtheria, 25 were white people. The public health significance of the endemic infection of the North American Indian and Metis people is discussed.