Exposure to allergens changes the way the airway responds to some stimuli (methacholine). The investigators will look at whether or not exposure to allergens changes the way the airway responds to a different stimuli (mannitol) and compare that with the known stimuli (methacholine).

Inclusion Criteria:

• mild, allergic asthma
• FEV1 greater than 70% predicted
• methacholine PC20 less than or equal to 16mg/ml

Exclusion Criteria:

• known sensitivity to mannitol or other excipient
• diagnosis of any other respiratory or non respiratory disease/disorder that would preclude the individual from participating
• recent thoracic, abdominal or eye surgery
• recent allergen exposure (4 weeks), respiratory infection (6 weeks)
• current immunotherapy
• pregnancy
• history of anaphylaxis
• use of asthma therapies other than short acting beta agonist