Eosinophilic granuloma limited to the lung has not to our knowledge been previously reported. Two histologically proved cases recently observed, and carefully followed, are recorded in the following pages. Eosinophilic granuloma involving both lung and bone, diagnosed by biopsy of the osseous lesions, has been reported on three occasions (6, 8, 9). To these three cases another is added. The cases presented here have all been confirmed by surgical biopsy and histologic study. This, we believe, is the first report of histologic confirmation of the lung lesion. Finzi (1), in 1929, recorded the first case of eosinophilic granuloma of the bone. His diagnosis was“a myeloma with preponderance of eosinophilic cells.” Otani and Ehrlich (5) and Lichtenstein and Jaffe (3) established the condition as an entity in 1940. Since these early descriptions there has been a tendency to expand the entity to include cases in which there are multiple bone lesions and even extra-osseous lesions, such as those involving lymph nodes, skin, lungs, and other organs (2). We feel that with the present report a further step is taken in this direction. Eosinophilic Granuloma Limited to the Lung Case I: A 32-year-old white male had a chronic cough developing during the winter of 1948–49, with the production of 50 to 120 c.c. of sputum daily. He complained of fatigue and night sweats but denied having fever or chills. A provisional diagnosis of pulmonary tuberculosis was made and he was admitted to Fitzsimons Army Hospital. He had lost 40 pounds in weight. He gave a history of dust exposure from September 1947 to January 1948. Physical examination was negative except for the presence of râles in both lungs. X-ray examination revealed a diffuse and patchy granulomatous type of pulmonary infiltrate (Fig. 1) widely disseminated throughout both lung fields, showing a peculiar nodular quality. The nodules ranged in size from almost miliary dimensions to 1.5 cm. in diameter. Their margins were hazy. They were made more apparent, or striking, by scattered areas of lucency interpreted as emphysema. In the background, throughout, the films showed a mild degree of fibrosis. The total white blood count was 18,500, with 83 per cent polymorphonuclear neutrophils but no eosinophils. A tuberculin (PPD, 1st strength) skin reaction was 1 plus; histoplasmin skin reaction 2 plus; coccidioidin skin test negative. Repeated examinations of sputum were negative for acid-fast bacilli and fungi. On Aug. 24, 1949, a left thoracotomy was performed. Lung tissue from the left lower lobe was submitted for examination.