Nucleic-acid amplification technology (NAT) assays have been implemented for HCV and HIV-1 in the United States, and many parts of Europe, Australia and Asia. Nucleic acid detection assays utilize many different technologies, and the WHO International Standards for nucleic acid tests are widely used to compare them. Currently, several laboratories are developing an assay for simultaneous detection of HCV RNA, HIV-1 RNA and HBV DNA. In the course of such development it was observed that the WHO International Standard for HIV-1 RNA (97/656) was positive for HBV DNA. In this report we confirm the presence of HBV DNA in the HIV-1 international standard through the qualitative Procleix-Ultrio assay. Further, using the TaqMan technology, through quantitative Bead Capture-TaqMan assay, we report that approximately 1000IU/ml dilution of HIV RNA contains approximately 4500IU/ml of HBV DNA.