In practice, breath and serologic tests are applied to confirm the diagnosis of H. pylori and for epidemiologic studies. The aim of the study is quantitative evaluation of the results of both tests in relation to the examined subjects' age, clinical symptoms and family history of gastric cancer. Investigations were carried out in 300 subjects, aged 16-70 years, 186 of them with asymptomatic H. pylori infection and 114 with family history of gastric cancer. The breath test was performed with 13C-labelled urea and Olympus FANci-2 analyzer and antibody titer was determined with ELISA in serologic test. The infection severity was the highest in the age group 31-40 years (result of the breath test 32.4+/-20.3/1000) and the lowest in the group aged 61-70 years (8.4+/-8.11/1000; p<0.01). The antibody titer was the highest at the age 21-30 years (89.6+/-39.5 U/ml) and significantly lower in the group over 60 years of age (31.0+/-27.2 U/ml; p<0.01). In subjects with asymptomatic infection the results of both tests were lower than in symptomatic infection in all age groups. No statistically significant differences were found between the subjects with and without family history of gastric cancer. H. pylori infection severity and immune response depend on the age of the examined subjects. H. pylori infection severity and immune response are lower in asymptomatic than in symptomatic subjects.