A novel probe was developed from genomic DNA ofHelicobacter pylori ATCC type strain 43629. Ithybridized with all 73 H. pylori clinical isolatestested but not with any of 183 non-H. pylori DNAs in dot blot hybridization. Typing tests revealed 41different HaeIII-digestion patterns from 57 H. pyloristrains tested. Based on the sequence of the probe, anested PCR was developed that detected as little as 2 fg of H. pylori DNA or approximatelyequivalent to one cell. No PCR products were amplifiedfrom any of 21 non-H. pylori strains tested. Using thisnested PCR, H. pylori DNA was detected in 33 of 45 (73%) saliva samples collected from patientswith gastric H. pylori infection. These data suggestthat the probe is useful for typing H. pylori and thatthe nested PCR is a valuable tool for detecting H. pylori DNA in saliva.