['Numerous studies have shown smoking and specific occupational exposures to be risk factors for bladder cancer. The risk of bladder cancer may be modified by the activity of carcinogen metabolizing enzymes. The glutathione-S-transferase Mu1 enzyme (GSTM1) detoxifies arylepoxides which are formed after exposure to certain polycyclic aromatic hydrocarbons and possibly aromatic amines. Approximately 40% of Caucasians lack GSTM1 activity due to a homozygous deletion of the GSTM1 locus on chromosome 1p13 (GSTM1 0/0 genotype). The aim of this study was to evaluate the combined effect of smoking and GSTM1 genotype on the risk of bladder cancer.', 'Sixty-one patients with transitional cell carcinoma of the bladder and 69 controls matched for age and sex were enrolled from the outpatient clinic. Lifestyle information was collected with a standardized questionnaire. DNA was extracted from white blood cells. The GSTM1 genotype was determined by a PCR-based method.', '92% of the 61 patients had a history of smoking compared with 81% of the controls. There was a significant dose-response relationship for pack-years of smoking (trend test: p = 0.003). The proportion of GSTM1 0/0 genotype among patients was 62% compared with 43% among controls (odds ratio = 2.1; 95% CI 1.1-4. 3). The expected interaction between smoking and GSTM1 genotype was not observed.'] Does a germline homozygote deletion of the glutathione-S-transferase Mu1 gene predispose to bladder cancer?