Associations between THMs and bladder cancer were stronger among subjects who were GSTT1 +/+ or +/− versus GSTT1 null (pinteraction = 0.021), GSTZ1 rs1046428 CT/TT versus CC (pinteraction = 0.018), or CYP2E1 rs2031920 CC versus CT/TT (pinteraction = 0.035). This evidence concerns the gene CYP2E1 and urinary bladder carcinoma.