Thirty three asthmatic subjects (>18 years, both sexes) who have stable asthma will be recruited to undergo methacholine challenges for a randomized, crossover, observational study. The objective of this study is to compare the methacholine PC20 of a modern delivery aerosol system, the Trudell AeroEclipse*II BAN nebulizer, to that of the current "gold standard", the English-Wright nebulizer. Subjects will inhale methacholine using both nebulizing systems on separate visits and the PC20 values will be compared. The results from these experiments will give us a better indication of whether the modern AeroEclipse* II BAN nebulizer might be sufficient to replace the current "gold standard" Wright nebulizer in clinical settings.