The combinations of the CYP1A1 inducibility and GSTM1 polymorphism have been investigated in relation to the histological type and peripheral or bronchial location of lung cancer in 54 surgically treated, current smoker lung cancer patients. The induced CYP1A1 was detected in 46 patients (85%) and the homozygous GSTM1 null genotype in 32 patients (59%). The role of CYP1A1 inducibility was found to be more important than that of GSTM1 polymorphism, because the non-inducible CYP1A1 was associated solely with bronchial tumours (P = 0.001), mainly squamous cell carcinomas. In patients with inducible CYP1A1, the expressing GSTM1 gene appeared to have a protective effect against contracting bronchial lung cancer, since 88% (14/16) of the lung tumours in this patient group were peripheral, whereas almost equal numbers of peripheral and bronchial tumours were observed in those patients lacking the gene (P = 0.037).