RESUMEN
The mitochondrial cytochrome c oxidase subunit I (CO I) gene and the second internal transcribed spacer region (ITS II) gene of Opisthorchis viverrini were compared among O. viverrini from various areas in northeast Thailand. The nucleotide sequences of partial CO I gene (417 bp) of O. viverrini differed among O. viverrini originated from Ubon Ratana, Leongpleuy, Ban Phai, Maha Sarakham, and Chatturat. These intraspecific variations were classified into 5 patterns but no area-specific pattem was observed. Amino acid sequence deduced from the nucleotide sequences of these genes was identical. Nucleotide sequences of a region of the O. viverrini ITS II gene (296 bp) from different areas were identical. However, they were different from those of Clonorchis sinensis, Haplorchis taichui, H. pumilio, Fasciola gigantica, Echinostoma malayanum and Centrocestus sp..