To examine whether genetic polymorphisms in Phase I and Phase II metabolic genes are associated with lung cancer risk, we studied 4 polymorphisms in the CYP1A1, GSTM1, GSTT1 and GSTP1 metabolic genes, individually and combined, in a large hospital-based case–control study of lung cancer including 789 lung cancer cases and 789 controls from a Caucasian population in Asturias, Northern Spain. This evidence concerns the gene GSTM1 and lung cancer.