Challenges will be carried out after a minimum 8-hour washout of short-acting ß2-agonist. Subjects will perform methacholine challenges on 2 separate days at the same time of day, at least 24-hours apart and all within a 2-week period. At V2, subjects will be randomly assigned to use either the Wright nebulizer or the AeroEclipse*II BAN nebulizer. Methacholine inhalation from the Wright nebulizer will be performed as follows. Subjects are instructed to wear noseclips and to breathe normally from the mouthpiece during the 2-minute inhalation period. Subjects inhale normal saline, then doubling concentrations of methacholine for 2 minutes each always starting at a dose of 0.03 mg/ml. Spirometry is measured with an electronic spirometer meeting ATS requirements. FEV1 is measured at 30 and 90 seconds after each inhalation and the highest FEV1 will be used to calculate the % fall from baseline. There is a 3 minute interval between the end of one inhalation dose and start of the next inhalation dose. The test is terminated when a fall in FEV1 of 20% of the baseline value occurs and the methacholine PC20 is calculated. The same protocol will be applied to methacholine inhalation using the AeroEclipse*II BAN nebulizer with the exception that the 2-minute tidal breathing will be reduced to 20 seconds and the interval between the end of one inhalation dose and start of the next inhalation dose is 3 minutes and 40 seconds. Subjects will return to the lab on V3 to complete a methacholine challenge using the alternate nebulizer from the one used on V2.