To investigate the pathogenesis of nasopharyngeal carcinoma, we tried to detect Epstein-Barr virus(EBV) in nasopharyngeal carcinoma by in situ hybridization. The detection of EBV in neoplastic cells of nasopharyngeal carcinoma may be also useful in diagnosis in nonendemic area. Cellular localization of viral genome in tissue section can be usually identified by in situ hybridization. But demonstration of EBV nucleic acids in formalin-fixed paraffin-embedded tissue sections is difficult and insensitive. We performed rapid colorimetric in situ hybridization for detection of EBV RNA using a bioinylated oligoprobe. The EBER1 probe is a marker of latent EBV infection. It was clearly demonstrated that EBV RNA is localized in neoplastic cells of undifferentiated carcinoma. These results demonstrated that detection EBV RNA using in situ hybridization is very sensitive and reliable method and clearly shows the relationship between neoplastic cells infected with EBV and expression of EBV genome.