The clinicopathologic features of five patients with acute eosinophilic pneumonia who presented with transient wheeze as well as acute onset of high fever, severe hypoxemia, and diffuse pulmonary infiltrates are described. Eosinophilic pneumonia was diagnosed by bronchoalveolar lavage and transbronchial lung biopsy. The illness resolved rapidly with or without corticosteroid therapy. No relapse occurred. To characterize the transient wheeze, a transbronchoscopic bronchial biopsy and pulmonary function tests were performed. Specimens of bronchial wall revealed eosinophil infiltration into the bronchial mucosa. Pulmonary function tests demonstrated reduced diffusing capacity and small airway dysfunction. These findings suggested that eosinophil infiltration into the bronchial mucosa might temporarily cause transient wheeze, different from bronchial asthma, due to small airway dysfunction in acute eosinophilic pneumonia.