Eosinophilic pneumonia has been defined as pulmonary infiltration of the lung by eosinophils that may or may not be accompanied by an excess of these cells in the peripheral blood. However, the concept of this disease and its nomenclature have not yet been established. In the present study, the clinical course of 11 cases of eosinophilic pneumonia, which were clinico-pathohistologically diagnosed and found not to be associated with organic disorders producing peripheral blood eosinophilia, were investigated extensively and compared with various types of eosinophilic pneumonia, as previously reported. Of five cases of acute eosinophilic pneumonia with a history (less than 1 month) of symptoms before diagnosis, a short clinical course, and no recurrence, four cases showed peripheral blood eosinophilia, and four cases did not require treatment with steroids. Of six cases of chronic eosinophilic pneumonia with a history (greater than 2 months) of symptoms before diagnosis, a prolonged clinical course, and recurrence, all showed peripheral blood eosinophilia, four cases required treatment with steroids, and four cases were recurrent. In one case with simultaneous occurrence of asthma and another case with asthma that occurred 4 years after the appearance of eosinophilic pneumonia, abnormal shadows on chest roentgenograms had continued for several years. These results suggested that various types of previously reported eosinophilic pneumonia classified by sex, the presence or absence of peripheral blood eosinophilia, the degree of clinical symptoms or peripheral blood eosinophilia, and the degree of abnormalities on the chest roentgenograms should be extensively reevaluated.