The aim of the study was to estimate the expression of CD20+ lymphocytes in the antrum mucosa in children, infected with Helicobacter pylori and after bacteria eradication. Biopsy specimens of gastric mucosa were the specimens, collected from 59 H. pylori-positive patients (Group I), 29 patients after H. pylori infection (Group II) and 18 H. pylori-negative children (Group III). The collected specimens were assessed for infection and inflammation and the expression of CD20+ lymphocytes was estimated, using mice monoclonal antibodies. The expression of CD20+ lymphocytes in the inflammatory infiltrate of the antrum mucosa correlated with the severity of gastritis, found in children with Helicobacter pylori infection and was the highest in comparison with the group of children after H. pylori eradication.