['To investigate the possible association of microsomal epoxide hydrolase (mEH) Tyr113His polymorphism with susceptibility to esophageal squamous cell carcinoma (ESCC) in a population of North China.', 'The mEH Tyr113His genotypes were determined by polymerase-chain reaction (PCR)-restriction fragment length polymorphism (RFLP) analysis in 257 patients with esophageal squamous cell carcinoma (ESCC) and 252 healthy subjects as a control group.', 'The frequencies for Tyr and His alleles were 44.2%, 55.8% in ESCC patients, and 44.0% and 56.0% in healthy subjects, respectively. No statistic difference in allele distribution was observed between ESCC patients and controls (chi2=0.008, P=0.929). The overall genotype distribution difference was not observed between cancer cases and controls (chi2=2.116, P=0.347). Compared with Tyr/Tyr genotype, neither His/His genotype nor in combination with Tyr/His genotype significantly modified the risk of the development of ESCC, the adjusted odds ratio was 1.076 (95% CI=0.850-1.361) and 0.756 (95% CI=0.493-1.157), respectively. When stratified for sex, age, smoking status and family history of upper gastrointestinal cancer, His/His genotype alone or in combination with Tyr/His genotype also did not show any significant influence on the risk of developing ESCC.'] Is epoxide hydrolase Tyr113His polymorphism associated with susceptibility to esophageal squamous cell carcinoma in population of North China?