Occupational immunologic lung disease can be identified both in the individual patient under laboratory conditions and in a population of workers in industry. Occupational airways disorder is the most common occupational immunologic pulmonary process and is a disease of the airways caused by the inhalation of a substance or material that the worker manufactures or uses directly or that is incidentally present at the worksite. There are several occupational airways disorders, including industrial bronchitis, occupational asthma, and reactive airways disease syndrome, the latter two of which will be discussed more thoroughly. Occupational asthma can be appropriately identified when the following are present: (1) typical symptoms, i.e., wheeze, cough, shortness of breath, and/or chest tightness; (2) specific identification of the offending agent; (3) documentation that the agent can cause asthma; (4) wheezes on physical examination; (5) pulmonary function changes; (6) immunologic abnormalities; (7) airway hyperreactivity; and (8) positive bronchial challenge with specific material. The diagnosis of occupational airways disorder requires a comprehensive approach, including clinical history, physiologic measurements, immunologic testing, and identification of airway hyperreactivity. By this approach both individual subjects and working populations can be studied.