 Within few days after a baseline exercise challenge, children was randomized to a double blind, placebo-controlled, three day doses, crossover study design. In practice each eligible patient was randomized by a computer-generated schedule to receive in sequence double-blind treatments with placebo or MNT 5 mg. Patients in sequence 1 received MNT, then crossed over to matching placebo; vice versa the case was for patients in sequence 2. Placebo and active treatments were separated by a 7-10 day wash-out period. Each child was assigned to one out of seven groups in order to perform the exercise challenge at different time intervals from drug administration which occurred always at 8.00 A.M. On day one the challenge was performed in the different groups 1, 2, 3, 4, 5, 6, and 8 hours after drug administration, respectively. Then treatment was continued as a single day dose for three consecutive days and a third challenge was then performed at the same time of the day. 