In this unit, protocols for growing Helicobacter organisms on plates or in liquid cultures are presented, followed by protocols for infecting mice with Helicobacter felis and H. pylori and for infecting ferrets with H. mustelae. Also, a procedure is described for adapting an H. pylori isolate to growth in mice. Support protocols describe methods for quantifying numbers of Helicobacter organisms, and how to create a growth curve for Helicobacter cultures. One important technique in investigating Helicobacter infection is assaying the disease processes that occur in the stomach, and a protocol is provided for preparing tissue sections for this purpose. It is also important to confirm that organisms recovered from tissue samples are, in fact, Helicobacter species, and a support protocol describes morphological and biochemical tests for this purpose. Helicobacter bacteria produce large amounts of the enzyme urease, and a support protocol describes how to perform a rapid urease test on animal-tissue biopsies. Assays of Helicobacter-specific immune responses require appropriate antigens, and preparation of both Helicobacter lysates and outer-membrane proteins are detailed for use in these assays.