Vacuolating toxin (VacA), cytotoxin-associated protein (CagA), urease and heat shock protein (HSP) are important virulence factors of H. pylori(HP).Infection by CagA+ HP is frequently characterised by heavy polymorph infiltration of gastric mucosa.The aim of this study was to investigate whether the severity and the activity of gastritis in patients with chronic renal failure (CRF) were associated with CagA+ HP infection and/or with a particular pattern of antibody response to the infection.A group of 51 patients was studied: 31 patients were on substitutive dialytic treatment (group A), and 20 were on conservative treatment (group B).The infection was diagnosed by histology and Western blotting (WB).Histology was carried out according to the Sydney's system.Serum antibodies to CagA, UreB and HSP were investigated by WB.Results: the prevalence of infec- tion was 76.4%; the prevalence was similar in the two groups; uninfected patients had a certain degree of gastritis activity; infected group B patients had a higher degree of gastritis activity than infected group A patients (P = 0.004); CagA seropositive patients did not have a greater activity of gastritis than CagAM patients (P = 0.540); group B patients with antibodies to UreB had higher degrees of gastritis activity (P < 0.001) and of gastric atrophy (P = 0.038) than group A UreB seropositive patients.These results suggest that, in CRF patients, the uremic microenvironment may interfere with pathogenic mechanisms of HP infection and CagA+ HP infection has no role in activity of gastritis.