The authors present the case of a 48 years old man having an exposure to irritant gases (azotic and lactic acids) in a closed space, inhaling them for 5 minutes. Shortly after the accident the patient displayed the signs of corneal and conjunctival burn; several days afterwards respiratory symptoms appeared: shortness of breath, dyspnea to minor efforts, then nocturnal dyspnea and orthopnea. Chest X-ray, CT scan, complex lung function tests and bronchoalveolar lavaje, together with the history of recent exposure to irritant gases led to the diagnosis of hypersensitivity obliterant bronchiolitis. Oral corticoids in dose of 60 mg/day determined a substantial clinical, radiological and functional improvement. The authors make some comments on the need of early diagnosis and efficient treatment.