GSTM1 and asthma: This review will discuss the three most researched classes of GST gene polymorphisms including pi 1 (GSTP1), mu 1 (GSTM1) and theta 1 (GSTT1), and summarize current knowledge on of complex mechanisms that may be involved in the interactions between household air pollution exposure and GST gene polymorphisms and potentially the aetiology of asthma in high risk populations who carry these risk alleles.