Background: Wide differing criteria are used to define the normal airway response to exercise, and as a consequence the estimated incidence of exercise-induced bronchospasm (EIB) in atopic children is wide. The purpose of this study was to establish normal range for changes in spirometry after exercise in children and then to use these normal values to assess the incidence of EIB in atopic children. Methods: Pulmonary function was assessed before, and 2, 5, and 10 min after 6 min of free running exercise in a group of 48 normal and 96 atopic children (70 asthmatics, 17 with allergic rhinitis, and 9 with atopic dermatitis/food hypersensitivity). Results: The EIB (defined as the normal group mean value -2 SD) occurred with a >10 percent fall in FEV1, >17.5 percent fall in peak expiratory flow rate (PEFR), >26 percent fall in mean forced expiratory flow during the middle half of the forced vital capacity (FEF25-75), and >40 percent fall in FEF25. Sixty-three of 70 asthmatic patients had EIB by at least one of these definitions, most marked at 5 min postexercise. The combination of FEV1 and FEF25-75 criteria enabled detection of all subjects with EIB. By FEV1 and FEF25-75 criteria, none of the subjects with allergic rhinitis or dermatitis had EIB. The fall in FEV1 after exercise in children with allergic rhinitis was within the range of normal, but with a significantly lower mean value than control subjects. Conclusions: EIB should be defined by using more than one maximum expiratory flow-volume curve parameter (ie, FEV1 and FEF25-75). The EIB (defined as a fall in FEV1 and FEF25-75) was only seen in asthmatic children and not in other atopic groups.