The incidence ofHelicobacter pyloriwas compared in high and low risk gastric cancer areas. Complete data were available on 116 age and sex matched sets of cases—patients with histologically proven intestinal metaplasia (IM)—and two control groups, one non-IM endoscoped controls (EC) and one non-endoscoped controls (NC) recruited from out-patient clinics.H. pyloristatus was determined by both serology and histology in individuals biopsied from three separate gastric sites. Our data show an increased incidence ofH. pyloriand intestinal metaplasia in areas at high risk for gastric cancer, good agreement onH. pyloristatus between histology and serology and a relationship betweenH. pyloristatus in individual biopsies and the degree of gastritis. With 116 matched sets of patients this is one of the largest series to date and supports the hypothesis thatH. pyloriinfection may be involved in gastric carcinogenesis through chronic gastritis and intestinal metaplasia.