 Our hypothesis is that swimmers with a positive bronchial provocation challenge have not necessarily an exercise-induced bronchoconstriction during swimming and the use of a bronchodilator will be unnecessary. Chlorine-derivatives exposure may be responsible for a weakness of the epithelium layer but warm and humid atmosphere of the swimming-pools may be protective for the development of a bronchoconstriction. Thus we also hypothesis that during a field test outside the swimming pool, swimmers will develop an exercise-induced asthma, and will need to take a bronchodilator in prevention. 