The exact pathogenesis of Helicobacter pylori infection is not fully understood. This study aims to evaluate the specific subset composition of peripheral blood lymphocytes in patients with H. pylori-positive duodenal ulcer n = 14), chronic antral gastritis n = 28), since reports so far have led to inconclusive and conflicting results. 42 patients with dyspepsia and 50 controls underwent the following procedures: 1) gastroscopy and gastric biopsy (five specimens) 2) histology, 3) serologic test for anti-H. pylori antibodies IgG (Pyloriset EIA-G, Orion Diagnostica) and anticytotoxin associated gene A (cag A) IgG antibodies (VIVA Diagnositika by ELISA), 4) analysis of the peripheral blood lymphocytes using monoclonal antibodies reacting with lymphocyte cell surface antigens (anti-CD3, anti-CD19, anti-CD4, anti-CD8, anti-CD16 + CD56, anti-HLA DR) by flow-cytometry (Becton-Dickinson) to detect possible changes in the lymphocytes subpopulations in patients with duodenal ulcer and chronic antral gastritis. We found no alteration in total T and B lymphocytes and CD4+ T, CD8+ T lymphocytes and natural killer cells of both duodenal ulcer and chronic antral gastritis patients compared to normal persons. Although there was a slight increase in the proportion of active T lymphocytes in duodenal ulcer and chronic antral gastritis groups comparing to healthy subjects the difference was not statistically significant. These data indicate that there is no systemic alteration in the specific immune system in response to H. pylori in patients with duodenal ulcer and chronic antral gastritis.