[Endobronchial actinomycosis].

A 63-year-old man was admitted to our hospital with obstructive pneumonia. The chest X-ray film and computed tomogram showed an infiltrative shadow in the right lower lung field. Examination with a fiberoptic bronchoscope showed a mass in the right basal bronchus. These findings suggested the diagnosis of lung cancer with obstructive pneumonia. Histopathological examination of a specimen obtained by transbronchial biopsy revealed sulfur granules with infiltration of neutrophils, which led to the diagnosis of endobronchial actinomycosis. After three months of treatment with penicillin, the mass disappeared. Comparison of bronchoscopic findings before and after penicillin treatment clearly showed the efficacy of therapy.