Phase 3. After a patient experiences a mild exacerbation or at the end of 8 weeks of steroid reduction and elimination, patients will enter the final phase of the study. At that time all patients will be instructed to increase their controller medication back to their baseline values. They will be followed for four weeks and repeat blood, urine, exhaled air and sputum samples will be obtained (Visit 4). Finally, subjects will be instructed to double their usual controller medication for four weeks after which repeat blood, urine and sputum samples will be obtained. Again, subjects will collect and store urine samples at a frequency of 3 times per week. The subjects will then be instructed to resume their usual asthma controller medication dosing and the study will be complete (Visit 5). All tests will be performed in the morning after an overnight fast.