DNA will be collected from patients participating in a parent clinical trial entitled: Effectiveness of Low Dose Theophylline as Add-On Therapy in the Treatment of Asthma (LoDo Trial). 627 patients from 19 Asthma Clinical Research Centers will be randomly assigned to receive placebo, or low dose theophylline (300 mg/day) or montelukast, 10 mg daily, for 6 months. Stepwise Linear and Poisson regressions will be performed on outcomes including treatment and genetic covariates, and interaction terms between treatment arm and genetic makeup. Polymorphisms that are highly associated with response can lead to the development of genetic tests that will identify patients most likely to benefit from montelukast treatment. This information may lead to individualization of asthma medications based on the genetic make-up of the patient.