In 380 histologically prepared biopsy specimens taken from the mucous membrane of the stomach, the employment of Giemsa staining and Warthin-Starry silver staining has revealed an often surprisingly abundant (i. e., to the extent of 66.1%) bacterial colonization of the surface of the gastric mucous membrane and of the gastric foveolae. The bacteria encountered here involve gram-negative and morphologically uniform flora of thin, S-shaped or slightly curved bacteria designated as campylobacter-like organisms (CLO). Evidence for Campylobacter pyloridis was also obtained in 55.1% of cultures from 49 native, microbiologically prepared gastric biopsy specimens. Bacterial colonization of the gastric mucous membrane by CLO is definitely correlated with inflammatory alterations in gastric membranes. Active forms of gastritis, however, are not more abundantly colonized by bacteria than are dormant forms. The positive correlation between inflammatory gastric alterations of various degrees and bacterial colonization of the gastric mucous membrane, furthermore, is not proof of an etiological relationship. These bacteria, obviously adapted to the mucus in the gastric foveolae and on the surface of stomach lining, are not evidence of an aggressive behavior or of penetration tendencies. Facultatively pathogenetic significance cannot, however, be excluded for bacteria occurring in such abundance in intimate epithelial contact. Pathogenetic influence of abundant colonization by CLO could well develop if additional noxae become effective.