We report on a 37-year old patient with a simple viral infection who presented with acute bronchitis with bronchospasm, a productive cough and severe dyspnoea. Because of his specific occupational history--the patient is a forester and was exposed to wood dust and fungi--he was at high risk for extrinsic allergic alveolitis with mucoid impaction, so that the cause of hypoxemia and cyanosis was obvious. Repeated immunological parameters including gel-precipitations were negative: The lung function pattern (reduced vital capacity, a reduced FEV1, reduced flow values at low vital capacity and with the characteristic shape of the flow volume-curve but normal airway-resistance) suggested the diagnosis of intrinsic asthma limited to the small airways - "bronchiolar asthma" - severe small airway disease.