In a survey of 930 adults aged 35-74 years randomly sampled from the general population of four areas of Italy, two at low and two at high risk for gastric cancer, plasma levels of Helicobacter pylori IgG antibodies were assayed in order to investigate associations with the geographical distribution of gastric cancer and other dietary and life-style factors, as assessed by personal interview. H. pylori positivity (antibody titer above or equal to 10 micrograms/ml), 45% overall, increased with age and was inversely associated with social class but showed little geographical variation or association with dietary variables and blood nutrients. H. pylori positivity was also associated with increased blood levels of pepsinogens, particularly pepsinogen II. The authors discuss these findings in relation to those from a previous case-control study of gastric cancer in the same areas.