We have studied 65 patients, who were treated with Bleomycin in this hospital, with regard to the pulmonary disorders induced by Bleomycin, and obtained the following results. Their early diagnosis and prevention were also discussed. 1) Pulmonary disorders, as side effects of Bleomycin, were recorded in 8 out of 65 cases (12%). They developed in the relatively old patients. The patients under 49 years old had no pulmonary disorders. There was no strict correlation between the development of side effects and the drug dose or the duration of administration. 2) The patients frequently had the subjective symptoms such as cough, sputum, and dyspnea. As for humoral factors, α(1)-acid glycoprotein and fibrinogen tended to show their high levels. Roentgenographically, the six cases revealed mainly funicular or patchy shadows in the lung field and the two, mainly fibrous reticular shadows. 3) Two of the patients with pulmonary disorders had previous lung diseases. The pulmonary disorders developed more frequently in the cases where the other anticancer drugs were used before and after the administration of Bleomycin. The disorders tended to appear frequently in the cases of malignant lymphoma. 4) The results shown above indicate that administration of Bleomycin requires careful consideration of its indication. It may be better to perform periobically chest roentgenography or pulmonary function test. When the development of pulmonary symptoms are detected, administration of Bleomycin should be discontinued immediately. Furthermore, it may be desirable to use, if possible, the fibroblast inhibiting agents together with Bleomycin.