Helicobacter pylori (H. pylori) is a human pathogen colonizing the human gastric epithelium in about half of the world´s population leading to peptic ulcer disease, atrophic gastritis and gastric cancer. Pathogenic strains of H. pylori possess several virulence factors, like CagA and VacA, correlating with higher gastric virulence and severely altered signal transduction. Recent studies have demonstrated the effect of H. pylori on gastro-intestinal microbiota leading to the progression of many intestinal as well as extra-intestinal diseases. The main goal of our study is to understand the effect of H. pylori colonization on the composition of the gut microbiota and on the progression of liver diseases. Our study has three specific aims: 1) Characterize the association between gastric microbiome and H. pylori pathogenic status from gastric biopsies; 2) Determine the lower intestinal microbiome from stool samples of the endoscopy patients; 3) Analyze the association between H. pylori -altered gut microbiota and liver functions. Nine patients undergoing upper endoscopy examination in West Tallinn Central Hospital (Tallinn, Estonia) will be enrolled in the study. The proposal is designed as a pilot study and will be highly valuable cornerstone for further research involving bigger sample sizes.