To provide the optimal test circumstances, some medications will be withheld for 8 to 96 hours before the bronchial provocation test: no short-acting bronchodilators, sodium cromoglycate, nedocromil sodium, or ipratropium bromide for 8 hours; no long-acting bronchodilators or antihistamines for 48 hours; no leukotriene antagonists for four days. Steroids should not be inhaled on the day of the test. No caffeine should be taken on the morning of the test. Vigorous exercise will be avoided for at least four hours prior to the start of the test as well as any exercise on the day of testing. Subjects will be scheduled for testing to allow at least 6-8 hours to elapse between previous vigorous activity and testing.