Exercise has been proposed as a useful challenge test for measuring bronchial hyper-responsiveness. The accepted diagnosis of exercise-induced asthma (EIA) is an end FEV1-change index of at least 10-20% post standard exercise. This preliminary study aimed to demonstrate the importance of the contribution of the small airways to the obstruction post-exercise. Ninety-one asthmatic children aged 6-17 years, of whom 70 had clinical presentation of EIA, participated in this study. They were subdivided into three groups according to the percentage fall index of FEV1 post an exercise challenge. Thirty-nine children showed a reduction of 35 ± 12% in FEV1, and a reduction of 50%, 55%, and 54% in FEF25%, FEF50%, and FEF75%, respectively. Thirty-one had a reduction of 12 ± 5% in FEV1, and a reduction of 21%, 29%, and 33% in FEF25%, FEF50%, and FEF75%, respectively. Twenty-one asthmatic children without clinical EIA demonstrated a percentage fall index in FEV1 (2 ± 2%) and a mean percentage fall in FEF25%, FEF50%, and FEF75% of 7%, 7%, and 6%, respectively. The results of the present study suggest that the end FEF50%-change index post exercise, at a cut-off point of 21%, may be superior to the currently accepted definition of EIA, which is based on end FEV1%-change.