Aims-To investigate the effect of eradication of Helicobacter pylori infection on gastric epithelial damage and gastritis, scored according to the Sydney system. Methods-Gastritis scores and epithelial damage were assessed in gastric biopsy specimens before, and five weeks and one year after anti-H pylori therapy in 66 patients with H pylon related gastritis. Results-The mean initial levels of activity, inflammation, atrophy, intestinal metaplasia, and H pylon scores were higher in the antrum than in the corpus or fundus. Eradication ofHpyloni resulted in an improvement in the mean inflanumatory score in antral biopsy specimens from 2-23 before treatment to 1*32 and 1-06, respectively, five weeks and one year after treatment. Corresponding values for fundic biopsy specimens were 1*30, 036 and 0-35. Activity scores improved from 1P41 before treatment to 0-13 and zero, respectively, five weeks and one year after treatment in antral biopsy specimens and from 0-60 before treatment to zero in fundic biopsy specimens. Before treatment, epithelial damage was present in 51% of biopsy specimens taken from the antrum and 23% of those from the corpus. Five weeks after eradication of H pyloni none of the biopsy specimens revealed evidence of epithelial damage. Conclusion-Eradication ofHpylon is followed by a rapid, significant improvement in the gastritis score and resolution of epithelial damage in antral and fundic mucosa.(J7 Clin Pathol 1995;48:250-256)