In situ hybridization using EBV encoded small RNAs (EBERs) probe and polymerase chain reaction (PCR) were performed to detect the presence of Epstein-Barr virus (EBV) genomes in 56 primary nasopharyngeal carcinomas. EBERs was detected in 46 cases(82%); 30 of 32 cases (94%) in differentiated non-keratinizing carcinoma (NKC, WHO-2) and 16 of 17 cases (94%) in undifferentiated nasopharyngeal carcinoma (UNPC, WHO-3). But none of 5 cases of squamous cell carcinoma (SCC, WHO-1) nor 2 cases of adenocarcinoma showed EBERs. EBV-DNA was also detected in 22 of 24 cases of NKC and in all 13 cases of UNPC by PCR but not in 3 cases of SCC or 2 cases of adenocarcinoma. This findings shows that the examination of EBERs and EBV-DNA is very useful, sensitive method in the detection of EBV.