We report on three patients who experienced persistent asthma symptoms after repetitive irritant exposure which took place over a period from several days to months. Airway inflammation was assessed by induction of sputum and functional follow-up information was obtained from serial lung function tests. All patients had bronchial hyperresponsiveness to methacholine at the time of diagnosis. However, induced sputum samples did not show increased differential count of eosinophils. Treatment with inhaled corticosteroids was started in all of the patients and two of them were removed from work. In the two patients who left the workplace, methacholine inhalation test became negative when symptoms disappeared, whereas the patient who continued working had persistent asthma symptoms and a deterioration of bronchial hyperresponsiveness.