A 35-year-old man had been exposed to the vapor of dimethyl sulfate which was split over the bed of a truck from an accidentally broken container. After receiving treatment at the critical care unit of our university hospital for respiratory failure, he was transferred to our ward with dyspnea persisting for one month. Chest X-ray showed diffuse nodular and infiltrative shadows and shadows suggestive of bronchial wall thickening. Bronchoscopy demonstrated tracheobronchial stenosis due to severe inflammation, and transbronchial lung biopsy revealed erosion and granulation in tissues of the bronchiolar walls. These findings suggested extensive inflammatory involvement of the respiratory tract extending from the trachea to the bronchioles. Treatment with antibiotics, especially agents with antipseudomonal activity, was effective against secondary pneumonia. Administration of corticosteroid for stenotic lesions of the airway was extremely beneficial. The clinical course of the respiratory lesion caused by dimethyl sulfate intoxication was following, including the bronchoscopic findings. The efficacy of treatment with corticosteroid and antibiotics was evaluated by successive bronchoscopic examinations of the lesions.