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Syphacia obvelata is a rodent nematode with high prevalence in laboratory mice. In the present study, we examined the genetic variability of S. obvelata from naturally infected laboratory mice in four different provinces, China. Five mitochondrial (mt) DNA regions, namely cytochrome c oxidase subunit 1 (p cox1), cytochrome b (p cytb), large subunit ribosomal RNA (p rrnL) and NADH dehydrogenase subunits 1 and 5 (p nad1 and p nad5), were amplified separately from individual nematodes by PCR, and then sequenced directly. The size of the sequences of p cox1, p cytb, p rrnL, p nad1 and p nad5 was 628 bp, 555 bp, 548 bp, 548 bp and 561 bp, respectively. While the intra-specific sequence variations within S. obvelata were 0-1.0% for p cox1, 0-1.6% for p cytb, 0-2.8% for p rrnL, 0-2.0% for p nad1 and 0-1.8% for p nad5, the inter-specific sequence differences among members of the Oxyuridae were significantly higher, being 14.0-17.5% for p cox1, 27.5-32.9% for p cytb, 35.8-37.2% for p rrnL, 22.2-26.8% for p nad1 and 22.3-25.2% for p nad5, respectively. Phylogenetic analyses based on combined sequences of four mt protein-coding genes, using Bayesian inference (BI), maximum likelihood (ML) and maximum parsimony (MP) methods, indicated that all of the S. obvelata samples grouped together with high statistical support, but samples from the same geographical origin did not always cluster together. These findings demonstrated the existence of low-level intra-specific variation in five mtDNA sequences among S. obvelata isolates from laboratory mice, but no obvious geographical distinction among S. obvelata isolates from laboratory mice in different geographic regions in China. These results provide basic information for further studies of systematics and population genetics of S. obvelata. [ABSTRACT FROM AUTHOR]