This report describes a patient with right lower lung (RLL) pneumonia of a subacute nature. Sputum and bronchial washings both grew N asteroides. Open lung biopsy showed bronchiolitis obliterans. Both the clinical and radiologic picture dramatically improved during three weeks of treatment with trimethoprim and sulfamethoxazole (TMP - SMX), indicating the possibility that N asteroides infection contributed to bronchiolitis obliterans pneumonia in this patient.