Associations between increasing quartiles of THMs and bladder cancer were stronger among subjects with GSTT1 +/+ or +/− versus −/−, GSTZ1 rs1046428 CT or TT versus CC, and CYP2E1 rs2031920 CC versus CT (no subjects had TT), with statistically significant interactions for each of the respective gene variants. Here, GSTZ1 is linked to urinary bladder carcinoma.