• Increases from visit pre-dose to each post-dose dose measurement in heart rate, blood pressure (systolic and diastolic). [ Time Frame: Days 0, 7, 10 ] [ Designated as safety issue: Yes ]
• Increases from visit pre-dose to each post-dose dose measurement in potassium and glucose [ Time Frame: Days 0, 7 ] [ Designated as safety issue: Yes ]

• FEV1 (percent change from visit pre-dose to each post dose measure) [ Time Frame: Days 0, 7, 10 ] [ Designated as safety issue: No ]
• FVC (percent change from visit pre-dose to each post dose measure); [ Time Frame: Days 0, 7, 10 ] [ Designated as safety issue: No ]
• FEF25-75% (percent change from visit pre-dose to each post dose measure); [ Time Frame: Days 0, 7, 10 ] [ Designated as safety issue: No ]
• Number of cumulative actuations received [ Time Frame: Days 0, 7, 10 ] [ Designated as safety issue: No ]

The purpose of this study is to compare the safety and tolerability of levalbuterol HFA metered dose inhaler (MDI) versus racemic albuterol HFA MDI.

A randomized, modified-blind active-controlled multicenter, two-way crossover study of HFA levalbuterol (without using a spacer) in subjects 12 years of age and older with asthma.

• Drug: Levalbuterol HFA MDI followed by Racemic albuterol HFA MDI
• Drug: Racemic Albuterol followed by levalbuterol HFA MDI

• Experimental:

  Subjects will receive both treatments: (a) levalbuterol HFA MDI; 45 micrograms (16 cumulative doses); followed by (b) racemic albuterol HFA MDI; 90 micrograms (16 cumulative doses).

  The first treatment will be administered, followed by a 7 ±2 days washout period, after which the second of the two treatments will be administered. Cumulative dosing will occur according to the following schedule: 1 puff at 0 and 30 minutes, 2 puffs at 60 minutes, 4 puffs at 90 minutes and 8 puffs at 120 minutes. All study drug will be administered directly without using a spacer for the entire study.

• Active Comparator: Subjects will receive both treatments: (a) racemic albuterol HFA MDI; 90 micrograms (16 cumulative doses) followed by (b) levalbuterol HFA MDI; 45 micrograms (16 cumulative doses) The first treatment will be administered, followed by a 7 ±2 days washout period, after which the second of the two treatments will be administered. Cumulative dosing will occur according to the following schedule: 1 puff at 0 and 30 minutes, 2 puffs at 60 minutes, 4 puffs at 90 minutes and 8 puffs at 120 minutes. All study drug will be administered directly without using a spacer for the entire study.

Inclusion Criteria:

• Subject, male or female, must be at least 12 years of age at the time of consent.
• Female subjects 12-60 years of age inclusive must have a negative serum pregnancy test at study start.
• Women of child bearing potential must be using an acceptable method of birth control throughout the study.
• Subject must have a documented diagnosis of asthma for a minimum of 6 months prior to study start.
• Subject must be in good health with the exception of their reversible airways disease and not suffering from any chronic condition that might affect their respiratory function.
• Subject must have a chest X-ray or had one within 12 months prior to randomization.
• Subject must be able to complete the diary cards and medical event calendars reliably on a daily basis, understand dosing instructions and be able to demonstrate good MDI administration technique. Any minor subject who is not able to do this must have a parent/legal guardian who can assist them during the study with these activities.

Exclusion Criteria:

• Female subject who is pregnant or lactating.
• Subject who has participated in an investigational drug study within 30 days prior to study start, or who is currently participating in another clinical trial.
• Subject whose schedule prevents him or her from starting study visits before 9 AM.
• Subject who has travel commitments during the study that would interfere with trial measurements or compliance or both.
• Subject who has a history of hospitalization for asthma within 4 weeks prior to study start, or who is scheduled for in-patient hospitalization, including elective surgery during the course of the trial
• Subject with a known sensitivity to levalbuterol or racemic albuterol, or any of the excipients contained in any of these formulations.
• Subject using any prescription drug with which albuterol sulfate administration is contraindicated.
• Subject with currently diagnosed life-threatening asthma defined as a history of asthma episodes requiring intubation, associated with hypercapnia, respiratory arrest, or hypoxic seizures within 12 months prior to study start.
• Subject with a history of cancer (exception: basal cell carcinoma in remission).
• Subject with hyperthyroidism, diabetes, hypertension, cardiac diseases or seizure disorders.
• Subject with a history of substance abuse or drug abuse within 12 months preceding study start.
• Subject with greater than 10 pack year history of cigarette smoking or use of any tobacco products within 6 months of study start.
• Subject with a documented history of bronchopulmonary aspergillosis or any form of allergic alveolitis.
• Subject who has suffered from a clinically significant upper or lower respiratory tract infection in the 3 weeks prior to study start.
• Subject with unstable asthma; or who have had a change in asthma therapy; or a visit to the Emergency Department or hospital for worsening asthma within 4 weeks.
• Subject who is a staff member or relative of a staff member.