SUMMARY The tuberculin test was administered to six groups of children in the Province of Cordoba, Argentina, and to a group of Minneapolis, Minnesota, children. Twelve hundred eighty-eight Argentina children and 2881 Minneapolis children were tested. In the Argentina group Koch's Old Tuberculin was used with the initial dose of 0.1 cc. of a dilution of 1:1000. For those who did not react, a second dose consisted of 0.1 cc. of a dilution of 1:100, and for those who still did not react, a third dose consisting of 0.1 cc. of a dilution of 1:10 was administered. In the Minneapolis group, the same procedure was employed except that the third dose was omitted. Among the Cordoba children the percentage of reactors to tuberculin ranged from 12.7 to 58.6, the average being 51.1. The low percentage of 12.7 was obtained among seventy-one children ranging from six to fifteen years of age, who resided in Pampa De Achala, where there is little contact with large centers of population. In the remainder of the Cordoba group the lowest percentage of reactors was 43.5. In the Minneapolis group of 2881 children, 23.1 per cent reacted definitely, and 0.6 per cent questionably to tuberculin. Among the 1288 Cordoba children, 741 had x-ray film inspection of the chest. Although no attempt was made to determine etiology from x-ray shadows, the films presented evidence of disease which was determined to be the first infection type of tuberculosis in the pneumonic stage in 6.9 per cent, and the reinfection type of pulmonary tuberculosis was diagnosed in 1.7. In 17.6 per cent, small, sharply outlined, dense shadows were seen in the pulmonary parenchyma, the hilum region, or both, which were thought to represent depositions of calcium, bone, or dense fibrous tissue. Among the 648 tuberculin reactors in the Minneapolis group the first infection type of tuberculosis in the pneumonic stage was found in 2.3 per cent. On the first examination the reinfection type of pulmonary tuberculosis was found in 0.2 per cent; however, on subsequent examinations this type of disease appeared in 1.1 per cent. Sharply outlined, small densities were seen in 21.1 per cent. Apparently the disease has the same characteristics among the children of the two nations, as they tolerate the first infection type of tuberculosis in the same manner and the reinfection type of disease is rare in this age group. The Pampa De Achala observations are unique. Here is an isolated community of families devoting their lives for the most part to the raising of sheep at an altitude of about eight thousand feet. Of 183 persons tested with tuberculin, the incidence of reactors was only 12.2 per cent among those of sixteen to twenty-five years of age. However, in the older age group, the incidence was 65.2 per cent, while the average for all ages was 32.2 per cent. Of the 116 persons in this group who had x-ray film inspection of their chests there was evidence of first infection type of tuberculosis in the pneumonic stage in 0.8 per cent, but in no individual was there any evidence whatsoever of the reinfection type of tuberculosis. Small, dense, sharply outlined shadows were present in 22.4 per cent.