Helicobacter pylori has been implicated in the genesis of human gastritis, dyspepsia, and peptic ulcers. However, its influence in the quality of experimental gastric ulcer healing has not been previously investigated. Standardized gastric fundic ulcers were produced in 50 male Sprague-Dawley rats (150-200 g) by a 4 mm in diameter focal, serosal application of 100% acetic acid. Thirty rats were administered 2 ml H. pylori suspension (urease producing, ATCC 43504) in normal saline (10(8) CFU/ml) 2x/day for 7 days. Twenty rats (controls) received 2 ml normal saline 2x/day for 7 days. Gastric ulcer surface area was measured under a dissecting microscope and mucosal specimens were obtained for qualitative and quantitative histology. No gross or microscopic duodenal abnormalities were identified at sacrifice. Ninety percent of control rats showed grossly and microscopically entirely healed ulcers. The remaining 10% showed partially reepithelialized ulcers (area, 0.78 to 1.77 mm2; mean, 1.27 +/- 0.7 mm2). The grossly "healed" mucosa demonstrated marked dilatation of gastric glands lined with mature surface epithelial cells. Parietal cells were scanty (5-10% of all cells). One hundred percent of the H. pylori-exposed rats showed persistence of chronic active ulcers (area, 1.76 to 19.63 mm2; mean, 8.95 +/- 6.15 mm2). The ulcer beds were infiltrated by acute and chronic inflammatory cells, abundant fibroblasts, and capillary networks. The raised ulcer borders were characterized by dilated glands lined by mature surface epithelial cells. Various special stains demonstrated the presence of H. pylori in the surface mucus and within the crypts.(ABSTRACT TRUNCATED AT 250 WORDS)