Epidemiological and laboratory studies investigating the role of allergen-pollutant combination as triggers of asthmatic attack have revealed that ozone, NO2, and aero allergens were independently or interactively related with asthma symptoms and changes in peak flow rates. The most familiar of these studies involving ozone and fungal spores revealed that they were co factors associated with increased asthma symptoms and inhaler use. The interesting observation that increased asthma admissions were associated with thunderstorms was originally attributed to peak fungal spore counts preceding or during the weather front but not to concomitant increases in air pollutants. Several more recent studies failed to show an associated with thunderstorms but instead found a positive association between asthma admission and higher levels of ozone at these times. As previously discussed, controlled challenge studies all have demonstrated that inhaled ozone, NO2, and SO2, individually or in combination, might enhance the airway response to inhaled allergens, thereby inducing asthma exacerbation.