Inclusion Criteria:

• Non-smoking male or female 18 60 years of age, with a previous diagnosis of asthma that has been stable for at least 4 weeks and which is unlikely to exacerbate during the study because of, for example, seasonal allergen exposure. Women of childbearing age must not be pregnant or nursing, and must be using an acceptable method of contraception.
• Ability to perform ATS/ERS-acceptable and reproducible spirometry7
• Screening FEV1 ≥70% of predicted for height, age, sex, and race when short-acting inhaled bronchodilators are withheld for at least 6 hours
• At least a 20% decrease in FEV1 after inhaling ≤4 mg/mL of methacholine (i.e., a PC20 FEV1 ≤4 mg/mL)
• Can be taught to use the dry powder device in accordance with the product's medication guide.
• If using an oral inhaled or intranasal corticosteroid, dosage must be stable for at least 4 weeks.

Exclusion Criteria:

• Allergy or sensitivity to inhaled methacholine, formoterol or to other β2 agonists
• Intolerance to other components of the inhaler or sensitivity to milk proteins
• Cigarette smoking in past year or >10 pack-year smoking history
• Respiratory tract infection within the last four weeks
• History of severe asthma attack requiring hospitalization in the previous 12 months
• Short course of oral and/or systemic corticosteroids in the past 4 weeks
• Inability to withhold caffeinated beverages for 12 hours or medications for appropriate intervals prior to each methacholine challenge
• Require treatment with beta-blockers (administered by any route), MAO inhibitors, tricyclic antidepressants, and/or maintenance therapy with systemic corticosteroids
• History and/or presence of pulmonary conditions (including but not limited to cystic fibrosis and bronchiectasis) other than asthma
• History of clinically-significant cardiovascular, renal, neurologic, liver or endocrine dysfunction. Patients with well-controlled hypertension, hypercholesterolemia or diabetes will not be excluded.
• If female, a positive urine β-HCG test
• Known or suspected substance abuse (e.g., alcohol, marijuana, etc.) and/or any other medical or psychological conditions that in the investigator's opinion should preclude study enrollment.