The antigenicity of Helicobacter pylori protein fractions separated by fast protein liquid chromatography size exclusion was investigated by EIA with sera from patients of well defined Helicobacter pylori status. The antigenic material of Helicobacter pylori was confined to fractions 8 and 14 to 21. Urease containing fractions (14/15) and flagella containing fractions (17/18) were identified. Fraction 8 non-specifically bound human immunoglobulin as demonstrated by the binding of Helicobacter pylori negative sera. The remaining fractions 14 to 21 when used individually as EIA antigens were 91-100% specific, however fractions 16 to 19 showed a reduced sensitivity (78%) compared with the acid extract (95%). The urease fractions were 91% sensitive. Purified urease antigen captured by antiurease monoclonal antibodies was 83% sensitive and 93.3% specific.