We evaluated the effect of genes involved in oxidative stress pathways (GSTM1, GSTT1, GSTP1, and NQO1), inflammatory response (TNFA), immunologic response (TLR4), and airway reactivity (ADRB2) on the association of traffic-related air pollution (using estimates of modeled NO2 exposure) and adult asthma in a large, multicenter population-based cohort. Here, GSTP1 is linked to asthma.