The Epstein-Bar virus (EBV)-encoded complementary strand transcripts (CSTs) are a recently described (1 ,2 ) group of related transcripts initiating from a common promoter that exhibit a complex splicing pattern and contain a number of small open reading frames with the potential to encode a number of proteins (3 ). The CSTs have been detected in most types of EBV infection, including nasopharyngeal carcinoma (NPC) (4 ), oral hairy leukoplakia (5 ), EBV-positive gastric carcinoma (6 ), and latently infected lymphoblastoid cell lines (7 ,8 ). The function of these transcripts is still unclear.