Forty-nine asymptomatic asthmatic children who showed exercise induced bronchospasm (EIB), received in a randomized double-blind fashion one of the four following drugs administered through nebulizer and facial mask: salbutamol 4 mg (13 patients), disodium chromoglycate 20 mg (12 patients), ipratroprium bromide 0.4 mg (12 patients), placebo (12 patients). They performed exercise fifteen minutes after receiving the drugs and spirometries were done 0, 5, 10, 15 and 20 minutes after the end of the exercise. Bronchodilation was noticed 15 minutes after the administration of salbutamol and ipratroprium bromide but not after cromoglycate or placebo. No patient receiving either salbutamol or cromoglycate had EIB whereas it occurred in 50% of those receiving ipratroprium bromide and 91.6% of those receiving placebo.