Of the bronchographic findings of 408 patients, performed in our hospital for recent 5 years, 108 cases showed definite bronchial obstruction, and 61 cases of those were selected and their obstructive findings were evaluated. All that not confirmed were abandoned. For evaluation of the reliability of 9 bronchographic obstruction signs onappplying to diagnose malignant or benign pulmonary diseases, each sign was identified and applied to each of the61 confirmed cases. In addition, obstructed bronchi, distance of obstruction from the bifurcation site, and thedirection of meniscus, if peresent, were evaluated. The reuslts were follows; 1. The most frequent cause ofbronchial obstruction was lung cancer (59.0%), and that of the benign obstruction was pulmonary tuberculosis(13.1%). 2. Amputation, asymmetric narrowing, thumbprint indentation, rat-tail narrowing and encasement signs werethe most accurate signs of malignancy and were practically diagnostic ones, 3, The most frequent sign in lungcancer was sharp cut off one, but it could be seen in lung abscess and in unresolved pneumonia, too. 4. Circumferential symmetric narrowing and regular concavity with a small central profection signs were specific onesto benignancy. 5. The most frequent obstruction sign in benign lung disease was gradual tapering sign, but it alsocould be seen inbronchogenic epidermoid and alveolar cell carcinoma. 6. Of all bronchial obstructions, 55.4% occurred at lobar bronchus and 77.4% of those were caused by lung cancer. 7. 77.2% of those obstruction which located within 3 times distance of the bronchial diameter at the nearest proximal bifurcation site, were lungcancer, but 75.0% of those located at over 3 times distance were benign pulmonary diseases. 8. There were nocorrelation of the direction of the meniscus at the obstructing and in differential diagnosis between benign andmalignant pulmonary diseases.