Helicobacter nemestrinae Bronsdon et al. 1991, a gastric helicobacter species isolated from a pigtailed macaque, is thought to be the species most closely related to the important human pathogen Helicobacter pylori. The only available strain of this taxon is the type strain, ATCC 49396T. We sequenced seven housekeeping genes and two flagellin genes for H. nemestrinae ATCC 49396T. If ATCC 49396T were a separate species, these sequences should have been distinct from those of H. pylori. Instead, all sequences clustered together with sequences obtained previously for 20 or more H. pylori isolates from diverse geographical locations. The 16S rDNA sequence differed from that reported previously for this strain by 38 nucleotides and was most similar to that of H. pylori 85D08 (accession no. U00769), which was isolated from a rhesus macaque. It differed by less than 1% from 16S rDNA sequences of numerous other H. pylori strains, including the type strain, NCTC 11637T (= ATCC 43504T). These data indicate that the strain currently distributed as H. nemestrinae ATCC 49396T is really a strain of H. pylori and that H. nemestrinae Bronsdon et al. 1991 is a junior heterotypic synonym of Helicobacter pylori (Marshall et al. 1985) Goodwin et al. 1989.