['To investigate whether the sequential therapy composed of high dose omeprazole and high dose amoxicillin in the first step was effective in eradication of H. pylori and whether there was a relation between effectiveness of the therapy and CYP2C19 gene polymorphism.', '134 dyspeptic patients with H. pylori were administered a modified sequential therapy composed of omeprazole 40 mg t.i.d. and amoxicillin 1000 mg t.i.d, for the first five days followed by omeprazole 20 mg b.d., metronidazole 500 mg t.i.d. and tetracycline 500 mg t.i.d, for the next five days. CYP2C19 genotype status was determined in patients. Hp eradication status was investigated by C14 UNT four weeks after treatment.', 'The eradication rates were 64.9% in ITT and 74.3% in PP analysis. In subgroup analyses, eradication rates were 73.8% and 60.8% (p: 0.145) in ITT for peptic ulcer and non-ulcer dyspepsia patients respectively and 86.1% and 69.1% (p: 0.052) in PP analysis for peptic ulcer and non-ulcer dyspepsia patients respectively. The difference was not significant. As for the CYP2C19 gene status, 81.5% of the patients had HoEM and 17.3% of the patients had HeEM, and eradication rates were 72% and 75% in ITT analysis for HoEM and HeEM respectively (p: 0.803) and 73.9% and 85.7% in PP analysis for HoEM and HeEM respectively (p: 0.347). There was not a significant difference in H. pylori eradication rates between the two groups.'] Is modified sequential Helicobacter pylori eradication therapy using high dose omeprazole and amoxicillin in the initial phase in the extensive metaboliser Turkish patients for CYP2C19 polymorphism ineffective?