We have recently observed six patients with acute interstitial eosinophilic pneumonia. All the patients suffered from an acute febrile illness and severe hypoxemia. Their chest films showed diffuse interstitial infiltrates. Kerley's A and B lines and pleural effusions are characteristic and important for the diagnosis of acute interstitial eosinophilic pneumonia, as they are frequently observed. Eosinophilia in peripheral blood was not initially present in any of the patients. Mild to severe eosinophilia was present during their convalescence. Histological examination showed eosinophilic infiltration of the alveolar walls and spaces. Half of the patients improved following treatment with corticosteroids, and the rest of the patients improved without treatment. To make an early diagnosis, this type of eosinophilic pneumonia should always be considered. It is important to recognize the radiographic findings, that is Kerley's lines and pleural changes, noted in this study. It should be noted that the number of eosinophils in peripheral blood has a tendency to be low during the acute phase.