The diagnosis of Helicobacter pylori (Hp) infection is an important goal in clinical practice. In this paper we evaluated 1. the analytical reliability of a new second-generation antigen based enzyme immunoassay (Cobas Core Anti Helicobacter pylori EIA) in detecting anti-Hp IgG antibodies, and 2. the behaviour of anti-Hp IgG in patients with chronic atrophic and non-atrophic gastritis as compared to healthy controls. The findings from the dilution curve, the values of intra and inter assay coefficients of variations (never above 10%) and of the recovery test (between 96 and 109%), confirm that the method is reliable. Serum IgG anti-Hp levels were found to be significantly higher in patients with histologically identified Hp infection, than in those negative at histology. Furthermore, the grade of histological positivity was correlated with serum IgG levels. However, we found a discrepancy between a low prevalence of Hp staining and a high prevalence of Hp seropositivity in patients with chronic atrophic or non-atrophic gastritis, but not in controls. This suggests that IgG serum determination may be more useful than histology in determining a present or previous infection in patients with chronic atrophic or non-atrophic gastritis.