Pulmonary alveolar proteinosis(PAP) is a disorder in which an insoluble, proteinaceous material, rich in phospholipid, is deposited on alveoli and bronchioles. Several cases were reported since 1986, and the numbers of patients is increasing in Korea. Although the pathogenesis and causative treatment of PAP is not well known, whole lung lavage is the only consistently successful treatment. We report 2 cases of PAP which were confirmed by open lung biopsy with electron microscopy and clinically improved by whole lung lavage with a review of literature.