Of the bronchograhic 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 90 braonchographic obstruction signs on applying to diagnose malignant or benign pulmonary diseases, each sign was identified and appled to each of the 61 confirmed cases. In addition, obstructed bronchi , distance of obstruction from the bifurcation site , and the direction of meniscus, if present , were evaluated. The results were follows : 1. The most frequent cause of bronchial obstruction was lung cancer(59.0%), and that of benign obstruction was pulmonrary tuberculosis(13.1%). 2. Amputation, asymmetric narrowing, thrumbprint indentation, rat-tail narrowing and encasement signs were the most accurate signs of malignancy and were practivally diagnostic ones. 3. The most freque t sign in lung cancer was sharp cutoff 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 projection signs were specific ones to benignancy. 5. The most frequent obstruction sign in benign lung disease was gradual tapering sign, but it also could be seen in bronchogenic epidermoid and alveolar cell carcinoma. 6. Of all bronchial obstructions, 55.4% occurred at lobar bronches 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 lung cancer, but 75.0% of those located at over 3 times distance were benign pulmonary disease. 8. There were no correlation of the direction of the meniscus at the obstructing end in differential diagnosis between benign and malignant pulmonary diseases.