This report investigated changes in pulmonary function, as well as the occurrence of symptoms, in potentially susceptible human subpopulations exposed to nitrogen dioxide. Drs. Morrow and Utell exposed healthy individuals and individuals with asthma, chronic obstructive pulmonary disease, and acute respiratory infection to air or 0.3 ppm nitrogen dioxide. The exposure period (four hours per day for five consecutive days) included defined periods of moderate exercise and pulmonary function measurements including spirometry, airway conductance, airway reactivity, and symptoms. Comparisons were made by disease state, exposure composition, and changes to individual base-line measurements.