Epstein-Barr virus(EBV) was detected by polymerase chain reaction(PCR) and dot blot hybridization in nasopharyngeal cancer tissues. The primer sequences used for PCR were those from the Bam W region of EBV genome. Since this region is repeated 10 times, higher sensitivity was expected than PCR results with primers based on other regions of EBV genome. Tissues from 31 patients with nasopharyngeal cancer(NPC) were examined. Among the 24 cases of undifferentiated carcinomas. EBV was detected in 22 cases(91.6%). Among 7 cases of squamous cell carcinomas, however, EBV was detected in only 3 cases(45.7%). This suggested the higher association of EBV in developing NPCs of undifferentiated types than those of squamous cell types. In 4 cases of neck node biopsies, EBV was detected more clearly than in occult cancer sites. EBV was also detected in 4 cases(20%) of non-NPC control nasopharyngeal tissues among 20 cases. The intensity of the amplified DNA of EBV from non-NPC control tissues, however, was not so dense as that from NPC tissues.