Thirty children 7-17 years of age with asthma and EIB, regardless of current asthma therapy will be eligible for this trial. Patients will receive 3-7 days of therapy with either montelukast (5mg or 10 mg capsule) or placebo tablets. After 3-7 days of therapy the patients will be crossed over to receive the alternative therapy. Exercise challenges will be completed at screening, baseline, visit 3 and visit 4. All patients will have an albuterol metered-dose inhaler (MDI) to be used on an as needed basis for asthma symptoms.