Glutathione-S-transferases are a group of phase II enzymes involved in the detoxification of xenobiotics in the lung.13 These enzymes play a role in the protection against oxidative stress since they influence the levels of glutathione, an important non-enzymatic antioxidant in the lung.14, 15 Variants in genes encoding glutathione-S-transferase mu 1 (GSTM1), theta 1 (GSTT1) and pi 1 (GSTP1) have been linked to decreased lung function and progression from increased BR to asthma,16–18 suggesting that these variants contribute to increased susceptibility to oxidative stress. Here, GSTM1 is linked to asthma.