A 55-year-old man was admitted with complaints of remittent fever (39 degrees C) and dyspnea on exertion which began ten days previously. His family and past histories were non-contributory for diagnosis except his occupation as a stone mason for 26 years. The chest X-ray film taken on admission showed diffuse small nodular shadows associated with small amounts of pleural effusion and bilateral hilar adenopathy. Arterihl blood gas analysis showed severe hypoxemia and hypocapnea (Pao2 32.2 Torr, Paco2 31.6 Torr). The serum level of LDH was 985 IU/L and ACE was 49.0 IU/L, lysozyme was 28.8 micrograms/ml. Biopsied materials of the lung obtained by TBLB, liver and bone marrow showed non-caseating epithelioid granuloma without caseating necrosis. T-lymphocyte ratio increased in BALF. The patient was diagnosed to have sarcoidosis. The administration of prednisolone was initiated, which resulted in a marked improvement of clinical data including chest X-ray films, BGA, LDH, ACE and lysozyme.