Inclusion Criteria:

• Subject's parent/legal guardian must give written informed consent, including privacy authorization, prior to study participation. Complete documentation regarding the consent process must be recorded in the case report form (CRF) and source documentation.
• Subject's parent/legal guardian must be willing and able to comply with the study procedures and visit schedules.
• Subject, male or female, must be between the ages of birth and <48 months, exclusive, at the time of consent.
• Subjects 24 to <48 months of age must have a history of physician-diagnosed asthma (defined as at least 3 episodes of respiratory symptoms consistent with asthma symptoms including, but not limited to, cough, wheeze, or dyspnea). Subjects 0 to <24 months of age must have a history of 3 episodes of respiratory symptoms that in the judgement of the investigator could be consistent with asthma or reactive airways disease
• Subject must be in good health and not affected by any other chronic conditions, including respiratory disorders other than asthma

Exclusion Criteria:

• Subject who requires or is expected to require any disallowed medications.
• Subject who has participated in an investigational drug study within 30 days, or who is currently participating in another clinical trial.
• Subject or parent/legal guardian who has daily commitments during the study that would interfere with trial measurements, compliance, or both.
• Subject who has a history of hospitalization for asthma, reactive airways disease, or bronchospasm within 4 weeks or who is scheduled for in-patient hospitalization, including elective surgery during the course of the trial.
• Subject who has experienced significant blood loss within 60 days of study drug.
• Subject with a clinical diagnosis of cystic fibrosis.
• Subject who was born prematurely, defined as less than 38 weeks gestational age at birth, and is <1 year of age.
• Subject whose body weight is less than 8.0 kg. This minimum weight requirement is based upon standard pediatric growth charts [CDC 2000].
• 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 levalbuterol or racemic albuterol sulfate administration is contraindicated.
• Subject with a history of life-threatening asthma, defined as previous asthma episodes requiring intubation or associated with hypercapnia, respiratory arrest, or hypoxic seizures.
• Subject with clinically significant abnormalities that may interfere with the metabolism or excretion of the study drugs or study participation (eg, abnormalities of renal, hepatic, metabolic, or endocrine function).
• Subject with a history of cancer.
• Subject with any chronic or congenital cardiorespiratory condition other than asthma including, but not limited to, bronchopulmonary dysplasia, congenital heart disease, and cystic fibrosis.
• Subject affected by an upper or lower respiratory tract infection in the 3 weeks prior to Visit 1.
• Subject with a history of ventilation for a respiratory condition occurring at or near birth, including those associated with prematurity or bronchopulmonary dysplasia. Ventilatory support for elective non-cardiopulmonary surgery is not exclusionary.
• Subject with any clinically significant abnormal laboratory values (hematology, blood chemistry).
• Subject with a clinically significant abnormal 12-lead ECG that would put the subject at risk for experiencing adverse cardiac effects.
• Subject who is a relative of a staff member.