Dose Response Study of Levalbuterol in the Prevention of Exercise Induced Bronchoconstriction Compared to Racemic Albuterol

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 must have a negative serum pregnancy test. * 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 for the study or within 12 months prior to randomization. * Subject must be able to complete the diary cards and medical event calendars reliably on a daily basis and understand dosing instructions. 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 of study start, or who is currently participating in another clinical trial. * Subject whose schedule prevents him or her from starting study visits before 12 PM. * Subject who is unwilling or physically unable to perform the exercise challenges as described in the protocol. * 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 that currently are not well controlled by medication or that may interfere with the successful completion of this protocol. * Subject with a history of substance abuse or drug abuse within 12 months preceding study start. Urine drug test must be negative at 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. * Subjects 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.