SummaryThe authors review the X Ray changes in 234 patients treated with streptomycin and dihydrostreptomycin. The action of the drug is very different, according to the radiological and clinical picture.A complete clearing of the X Ray film has been observed in the following groups :—Miliary Tuberculosis : 100 %.—Miliary Tuberculosis with irregular granulations : 44 %.—”Cold miliary”: 30 %.—Reticular and nodular lesions : 8 %.—Large and irregular shadows : 11 %.—Homogeneous shadows : 9 %.—Cavities : 3 %.Generally, the acute cases respond better than the chronic ones. When there is a cavity, the drug is less active on the associated lesions of the lung. In this case, a complete clearing is uncommon. Good results are obtained in bronchial tuberculosis.The disappearance of the T. B. in the sputum was seen in 10 % of the cases with cavities, and in 50 % of the cases without cavity.The authors discriminate imperative, relative, and questionable indications.The use of streptomycin, associated with collapsotherapy makes more safe this procedure, and allows to extend the indications of the latter.Toxic reactions are less common with dihydrostreptomycin than with streptomycin, but at high dosages (100 grs), are still observed.