A 44 year old man was admitted complaining of exertional dyspnea. The patient denied denied any occupational history of hard metal exposure. Chest radiography showed an increased interstitial marking at the peripheral po rtion of both lower lung fields. The spirometric values were within the normal ranges. However, the diffusion capacity of the lungs was lower. In the bronchial lavage fluid, the characteristic multinucleated giant cells were noticed, and the macrophage compartment was 96% and the neutrophils were 4%. Highresolution CT scan revealed ground glass opacities with emphysematous lung changes at the peripheral portion of the whole lung. An open lung biopsy confirmed the presence of numerous multinucleated giant cells (Define GIF) with an associated interstitial fibrosis throughout the lung. The radiographic abnormalities and symptoms subsequently improved following treatment with oral corticosteroids.