OBJECTIVE We tested if host gastric Lewis antigens and the babA2 genotype of Helicobacter pylori correlated with clinicohistological outcome. METHODS We enrolled 188 dyspeptic patients (45 with duodenal ulcer, 45 with gastric ulcer, and 98 with chronic gastritis) with H pylori infection, proved by culture and gastric histology, reviewed by the updated Sydney system. Gastric expression of Lewis (Le) antigens Le(a), Le(b), Le(x), and Le(y) was determined immunochemically to determine intensity (range 0-3). The corresponding 188 H pylori isolates were screened for babA2 genotype by polymerase chain reaction. RESULTS All H pylori isolates had a positive babA2 genotype. We identified Le(a) in 33.5%, Le(b) in 72.9%, Le(x) in 86.2%, and Le(y) in 97.4% of biopsies from these 188 patients. Patients who expressed Le(b) had a higher H pylori density than those who did not express Le(b) (p<0.001). Among 139 patients who expressed Le(b), H pylori density increased with a higher Le(b) intensity (p<0.05). Gastric atrophy decreased with Le(b) intensity and thus resulted in lower H pylori density in the antrum (p<0.05). For the 49 patients without gastric Le(b) expression, H pylori density was positively related with Le(x) and Le(a) expression (p<0.05). CONCLUSIONS Taiwanese H pylori isolates are 100% babA2 genopositive. Gastric Le(b) as well as Le(x) intensity may be major determinants of H pylori density. While lacking gastric Le(b) expression, Le(x) and Le(a) were closely related to H pylori colonisation.