Early attempts to identify non-human reservoirs for Helicobacter pylori were largely unrewarding. The one exception being old-world macaques, which were found to be colonized with H. pylori; however, it is doubtful whether this species provides an important reservoir for human infection. The possibility of other animal reservoirs and zoonotic transmission of H. pylori has been discussed, but until recently has not received serious study. Enthusiasm to initiate extensive studies in this area were further dampened by the inability to experimentally infect several different species of mammals with the organism. Reports using whole-cell enzyme-linked immunoabsorbent assay (ELISA) sonicate to monitor infection serologically, have cited a high incidence of H. pylori infection in abattoir workers. These results have been criticized because of potential antigenic cross-reactivity in workers' sera due to the constant exposure of these personnel to other gastrointestinal flora of animals. The large spiral gastric Helicobacter-like organisms (GHLOs) commonly noted in dogs and cats are associated with approximately 0.08-1% of gastritis in humans. These GHLOs often infect patients who own pets, suggesting a zoonotic link. Thus, the recent isolation of H. pylori from the inflamed gastric mucosa of commercially reared cats, and the ability to experimentally infect cats with H. pylori, raises the possibility of zoonotic H. pylori transmission from infected animals who have close human contact. Water and raw vegetables have been linked with H. pylori transmission in a few epidemiologically-based studies in developing populations. The recent isolation of H. pylori from the faeces of adults and children implicates a faecal-oral transmission pathway and supports the theory that both food and water (via faecal contamination) could be a source of H. pylori. Providing conclusive evidence that H. pylori has the ability to exist in the environment as a viable, non-culturable coccoid form that can replicate after ingestion by a mammalian host would considerably strengthen the hypothesis that water and food are important H. pylori reservoirs. The existence and extent of these reservoirs in nature, and the manner in which they interact with humans, will provide important new insights into understanding the epidemiology of this worldwide infection.