Dehydration of the respiratory epithelium has been identified as a possible cause of exercise-induced bronchoconstriction (EIB). The aim of study was determine the effects of body dehydration on EIB. We measured FEV1, FEV1/FVC and FEF25-75 in 19 university soccer players (age: 20.5 ± 2 years) at 5, 10 and 15 minutes after exercise in hyperthermic conditions, with and without hydration. A 47.3% of the dehydrated group developed bronchoconstriction at 5 minutes post-exercise, 42.1% continued with this condition at 10 minutes and 26.3% kept it after 15 minutes post-exercise. None of the subjects rehydrated developed EIB. Results allow us to infer that some athletes are at risk for reduced lung function by more than 2% of body weight.