A 46-year-old man was admitted to the hospital because of chest pain and left pleural effusion. Fever and dyspnea developed on the third hospital day. Interstitial shadows and pleural effusions in both lower lung fields appeared on chest roentgenograms. Microscopic examination of transbronchial lung biopsy specimens taken on hospital day 5 showed thickening of the alveolar walls and desquamation of macrophages into the alveolar spaces. Analysis of bronchoalveolar lavage fluid revealed many cells and macrophages. Tests for anti-nuclear antibody and anti-DNA antibody were positive, which, in addition to serositis and proteinuria, established the diagnosis of systemic lupus erythematosus. The interstitial shadow on chest roentgenograms was believed to have reflected an acute pulmonary manifestation of systemic lupus erythematosus. The symptoms and the abnormality on chest roentgenograms were relieved within 1 month of the start of pulse therapy with prednisolone.