A single intravenous injection of zileuton (150 or 300 mg) will be administered to patients with stable asthma. The goals will be to determine if zileuton i.v. can produce a rapid increase in FEV1/PEFR and when this effect can be seen. The safety of this route of administration of zileuton will also be studied. PK will be obtained in a population based method.

Inclusion Criteria:

1. Male or female patients 12 years of age or older
2. Diagnosis of asthma by current ATS guidelines
3. FEV1 of 4-80%.
4. Reversibility of at least 13% after bronchodilator treatment
5. Must be willing to with hold SABA for 6 hours and ICS for 24 hours prior to treatment.
6. Informed consent

Exclusion Criteria:

1. Females of child bearing potential unless using birth control
2. Uncontrolled systemic disease
3. Known hypersensitivity to zileuton or components of zileuton injection.
4. Upper or lower respiratory tract infection within the last 2 weeks
5. Admission to hospital or ER visit for asthma exacerbation within the last 3 months
6. Course of oral or parenteral steroids within the last 3 months
7. Current smoker or H/O > 15 pack years
8. Creatinine > 1.5 x ULN
9. ALT > 3 x ULN
10. BP < 100 (systolic)
11. H/O HIV
12. H/O alcohol or drug abuse
13. Patients taking Xolair, theophylline, montelukast, zafirlukast, nedocromil, cromolyn sodium, Zyflo (within the past 7 days), warfarin, propranolol, inhaled anti-cholinergics, or LABA.
14. Pregnant or breast feeding females
15. Current participation or participation in an experimental drug study within 30 days.