Inclusion Criteria:

• Documented physician diagnosis of moderate to severe, persistent asthma, defined in the National Heart, Lung, and Blood Institute (NHLBI) guidelines as FEV1 < 80% predicted for height, age, and sex or a history of FEV1 < 80%
• Between 6 and 75 years old at the time of screening (Visit 1 [Week -2])
• Current treatment with the following medications: Moderate doses of any inhaled steroid preparation on a daily basis for at least 30 days prior to screening; and/or oral steroids at a stable dose on a daily basis for at least 30 days prior to screening; and currently treated with at least one of the following drugs on a daily basis at a stable dose for at least 30 days prior to screening: long-acting β-adrenergic (salmeterol), leukotriene receptor antagonist (LTRA), xanthine derivatives, or sodium cromoglycate
• Signed informed consent (in the case of a minor, consent must have been given by the child's parent or legal guardian)
• Serum IgE level of ≥ 30 IU/mL and ≤ 1300 IU/mL and a body weight ≥ 20 kg and ≤ 150 kg and fell within the protocol-defined dosing table ranges
• For females of childbearing potential, in the opinion of the investigator, use of an effective method of contraception to prevent pregnancy and agreement to continue to practice an acceptable method of contraception for the duration of their participation in the study
• Willingness to participate fully for the duration of the study

Exclusion Criteria:

• Current active AEE defined as requiring initiation or increase in oral steroid dose or treatment with at least a doubling of inhaled steroid dose
• Thrombocytopenia as evidenced by platelets < 100,000/uL
• Pregnancy or lactation
• Previous randomization in this study
• Use of any experimental drug within 30 days prior to study screening
• Known hypersensitivity to any ingredients of Xolair, including excipients (sucrose, histidine, polysorbate 20)
• Diagnosis of aspirin or nonsteroidal anti-inflammatory drug-induced asthma
• Active lung disease other than asthma (e.g., chronic bronchitis, emphysema, cystic fibrosis, chronic obstructive pulmonary disease)
• History of smoking within 2 years of the study screening visit or history of smoking ≥ 10 pack years
• Significant systemic disease (e.g., infection, hematologic, renal, hepatic, coronary heart disease or other cardiovascular diseases, endocrinologic or gastrointestinal disease) within the previous 3 months
• History of neoplasia
• History of noncompliance to medical regimens
• Any systemic condition requiring regular administration of immunoglobulin