We have succeeded in inducing pulmonary disorders in mice and rabbits by administering Bleomycin. The following conclusions were obtained from microscopic and electronmicroscopic observation. 1) Pulmonary disorders could be induced in two different species of animals, mice and rabbits. The histological changes consisted of hypertrophy of the alveolar septum, precipitation of fibrin, proliferating tendency of the bronchiolar epithelium, and septal interstitial cellular infiltration. These changes were found to be localized initially under the pleura and appeared to proceed diffusely into the deep region of the lung. 2) The present findings suggested, as for the mechanism for development of pulmonary disorders, that Bleomycin gives vascular endothelial cells direct damages which increase the permeability of the blood vessels. Then the alveolar space and interstice begin to contain the protein-rich exsudate owing to the increased vascular permeability. Disturbance of absorption would cause fibrotic changes. Additional bacterial infection would sometimes further increase vascular permeability and make the histological pictures appear to be more complicated.