Four barrier-born pigs were inoculated with Helicobacter pylori during gastroscopy. Infection in all pigs was established after 3 weeks, and the animals were kept isolated from other pigs in ordinary experimental sites. The pigs were sacrificed and examined 3, 5, 6, and 6.5 months postinoculation. A detailed urease mapping of the pig stomachs showed a patchy distribution of H. pylori. The bacteria colonized in all pigs, with a concentration of H. pylori-positive areas in the antrum and fundus. Furthermore, the number of colonized areas tended to increase with time, and some of these areas showed a strong urease reaction, indicating a heavy colonization with H. pylori. Biopsies from these areas contained 10(2) to 10(5) CFU per 2-mm-wide biopsy. We conclude that persistence of H. pylori infection in barrier-born pigs can be demonstrated for at least 6.5 months. The patchy distribution and the variability of viable bacteria were similar to those described for humans.