Based on the knowledge that metabolic genes are presumed to modulate an individual's susceptibility to cancer by interacting with carcinogens, and since the inheritance of several unfavourable genotypes is supposed to additionally increase the risk of gastric cancer [8,9,11], this hospital-based case-control study aims to investigate the effect on gastric cancer of selected SNPs of CYP1A1, CYP2E1, mEH, GSTM1, GSTT1, NAT2, SULT1A1, and their differential effect according to tobacco smoking and alcohol habits. The gene discussed is EPHX1; the disease is gastric cancer.