CYP2C19 genotype has recently been shown to have an impact on peptic ulcer healing, H. pylori eradication and therapeutic effi cacy of proton pump inhibitors. CYP2C19 genotypes can be determined by polymerase chain reaction and restriction fragment length polymorphism analysis and are classifi ed as rapid metabolizer (RM), intermediate metabolizer (IM) or poor metabolizer (PM). In patients that carry RM genotype the eradication rate by triple therapy was signifi cantly lower than those with PM genotype (97.8% vs 72.2%: P < 0.01). Recent study in Thailand demonstrated the prevalence of CYP2C19 genotype: 37.2% in RM, 53.7% in IM and 9.1% in PM. Multidrug resistant is a growing problem worldwide and might have an impact on the effi cacy of eradication therapy. Our recent studyshowed that multi drug resistant H. pylori has increased from 3% in 2005 to 5.5% in 2010. Our previous study also showed that levels of IL1β, IL6, IL8 proinfl ammatory cytokines were higher in H. pylori-positive than in H. pylori-negative patients. It has been shown that IL-1 polymorphism is a risk factor for disease development rather than its impact on treatment outcome. Our study also showed that cagA 2a gene was signifi cantly higher in metronidazole resistant than in metronidazole sensitive strains (100% vs 74.1%; OR = 4.8, 95% CI = 1.2–26.8, P = 0.01). cagA 2a gene might be related to metronidazole resistant strains of H. pylori infection in some areas such as Thailand.