An Opisthorchis viverrini specific repetitive DNA fragment was isolated from the O. viverrini genome. The cloned fragment, herein designated pOV-A6, contained tandemly repeated 334 bp O. viverrini DNA and has the potential to be a highly specific and sensitive DNA probe. Radioactively labelled pOV-A6 could detect as little as 25 pg of its own genomic DNA and five purified eggs by dot-blot hybridization. The presence of 50 O. viverrini eggs could be readily detected in samples containing faecal materials. The probe was highly specific for O. viverrini DNA and did not cross hybridize with DNAs prepared from related and unrelated parasites, enteric bacteria and a number of definitive and intermediate hosts. The probe has potential for screening a large number of samples and could be readily applied in epidemiological studies.