A 52-year-old man was admitted to our hospital with high-grade fever, dry cough and severe dyspnea. Chest X-ray films revealed diffuse small nodular shadows in all lung fields, prominently in the middle and lower lung fields. On examination, peripheral blood eosinophilic leukocytosis and severe hypoxemia were demonstrated. His clinical condition improved during five days after the admission without any therapy but oxygen inhalation. The abnormal shadows decreased in several days, and disappeared completely in thirty days. Bronchoalveolar lavage fluid revealed increased total cell counts, mostly with eosinophils (60%) and lymphocytes (21%). Histologically, the transbronchial lung biopsy specimen showed that the walls of pulmonary arteries and bronchioli were markedly infiltrated with eosinophils, and that alveolar septa were edematous with mononuclear and eosinophilic cells infiltration. There were no prominent changes in the alveolar lumen except few macrophage exudates. Our case was of importance for two reasons: first, eosinophilic pneumonia could take the form of interstitial pneumonia both roentgenologically and histologically; second, Crofton's classification of P.I.E. could not be applied to this case.