By oral administration of the eggs of ascaris to guinea pigs and rabbits, the animals were infected, or reinfected, or reinfested after sensitizing them with ascaris emulsion; and the blood picture. the roentgenograms of the lungs as well as histo-pathological findings of respective groups were comparatively studied. The results obtained are described below. 1) In blood picture ebsinophilia has been recognized in all the cases, whereas it is most marked in the cases where the animals are reinfested after the sensitization with ascaris emulsion. 2) When a large amount of ascaris eggs is given in the first administratios the shadows like pneumonia or nodular shadows are revealed in the roentgenograms of the lungs while in the cases of super infect or reinfection only, the appearance of these shadows is on the whole quicker and relatively more nodular shadows are observed as compared with the former. Of the four cases receiving the ascaris eggs after sensitization with the emulsion of ascaris, one case presented a picture of transitory infiltration in the lungs. 3) In the primary infection cases, hyperemia and hemorrhages are generally the main findings at early stage but later on the hypertrophy of alveolar septum can be recognized due to the infiltration of neutrophils, eosinophils, lymphocytes, and moncytes and the hypertrophy and proliferation of alveolar epithelium. In the cases reinfected or reinfected after the sensitization with the ascaris emulsion, the swelling and hypertrophy of blood-vessel wall and edemas in the perivascular space are more marked than the former, and likewise the nodular cell infiltration and the appeareance of giant cells are more striking than in the first infection cases. Grannloma formation can also be recognized in the latter. 4) From these findings it has been found that the ascaris allergy plays one of the pathogenetic roles in the transitory infiltration of the lungs.