GSTM1 null genotypes (OR: 2.35, 95% CI 1.48, 3.75) were associated with increased risk of asthma, GSTP1 with Val/Val alleles (OR: 0.39, 95%CI 0.19, 0.80) were associated with decreased risk of asthma compared with those with Ile/Ile genotypes. No evidence of GSTT1. Here, GSTM1 is linked to asthma.