There is a great need to develop molecular techniques for the typing of Helicobacter pylori isolates since classical bacteriological assays, such as serotyping or lysotyping, are lacking. Such techniques would provide the microbiologist with the tools necessary to differentiate one strain from another one (essential for epidemiological studies), to determine whether individuals might be colonized by several isolates, and to elucidate whether ulcer relapse following treatment is associated with the colonization of the gastric mucosa by the same isolate or is caused by reinfection.