This paper includes 50 dogs, differing in breed and sex, from 3 months to 12 years of age: 26 samples of endoscopic stomach biopsies were taken from ill animals which displayed chronic vomiting, 12 endoscopic biopsy samples of healthy dogs and 12 stomach samples of autopsied dogs. Helicobacter spp. and Gastrospirillum hominis findings were confirmed in 20 of the 26 ill dogs, 8 of the 12 autopsied animals, and 2 of the 12 healthy animals by histopathology and direct gastric tissue smears. In 26 endoscopic biopsies various clinical and endoscopic findings (7 cases of erosive and 4 of ulcerous gastritis, 12 cases of chronic gastritis and 2 of gastric reflux) were previously determined. Histopathological examination of stomach mucosa of 5 autopsied and Helicobacter positive dogs determined focal lymphocyte infiltrations, mainly located in the subglandular region. Along with such lymphocyte accumulations, in certain cases a diffuse infiltrate consisting of eosinophilic granulocytes and plasma cells was also present. In most biopsied samples, stained with hematoxylin-eosin, histopathological changes were not observed, except in 5 dogs where diffuse lymphocyte infiltration of the mucosa was noted and in two dogs with signs of chronic gastritis, that is hypertrophy and stratification of the mucosa epithelium, and with lymphocyte and plasmocyte infiltration. By modified Giemsa staining of 20 of the endoscopically biopsied animals, spiral microorganisms with varying numbers of spiral curves were observed, which were similar to the necropsy stomach mucosa samples, belong to various types of Helicobacter spp, and some of them morphologically correspond to Gastrospirillum hominis.