A 46-year-old man with chronic myelogenous leukemia (CML) was admitted to our hospital because of high fever. The chest radiographs showed bilateral groundglass-like infiltrates in the perihilar region. Transbronchial lung biopsy (TBLB) and autopsy revealed PAS-positive granular materials characteristic of pulmonary alveolar proteinosis (PAP). He had received interferon-alpha since the time of CML diagnosis. Busulfan had never been administered. Altered cell-mediated immunity was thought to be closely related to the development of PAP.