The diagnosis of eosinophilic pneumonia can be made clinically based on the history, course of the disease, and the presence of croup in both lungs, as well as increased peripheral blood eosinophils on blood tests and chest radiographs. Atypical cases can be diagnosed pathologically by lung biopsy and, if necessary, by treatment with a prednisone test. Eosinophilic pneumonia is mainly an alveolar and interstitial, eosinophil-dominated infiltrate. The main clinical manifestations are allergic rhinitis or a history of nasal polyps in 1/3 to 2/3 of patients, and adult-onset asthma or other respiratory symptoms in 2/3 of patients. It is common to have a low-grade fever, night sweats, moderate weight loss, a cough and, rarely, mucus sputum, and in a small percentage of patients, hemoptysis. Patients will eventually develop progressive dyspnea, and a small percentage will develop acute respiratory failure or acute respiratory distress syndrome. laboratory tests will show an increase in blood leukocytes greater than 10 x 10^9 cells/L. 60-90% of patients will have an increase in peripheral blood eosinophils greater than 60%. However, the lack of peripheral blood eosinophils does not completely exclude the disease, as more eosinophils can be found in the sputum and the hematocrit is increased.