Background: Nasopharyngeal carcinoma (NPC) is endemic in certain geographic regions, such asSoutheast Asia, and is associated with several environmental and genetic factors. Undifferentiated NPCis consistent with Epstein-Barr virus (EBV) infection. NPC is the most common ENT tumor in Indonesiawith high prevalence among native populations and yearly overall incidence estimated 6.2 per 100.000 population. Purpose: To explain the advantage of EBV immediate-early gene expression analysis indetermining of NPC diagnosis and management of NPC.Review: Replication of EBV implies to twocellular reactions, i.e. latentcy and lytic cycle expression of EBV lytic genes which consists of three lyticphases, i.e. immediate-early, early and late phase. Expression of immediate-early genes BZLF1 andBRLF1 are needed to induct of early and late genes, so both genes are known as transactivator genes.BALF1, an early lytic gene, expresses some protein regulating EBV replication in NPC. Expression of BCLF1, a late lytic gene, is essential for EBV replication, particularly in the forming of virion structure inNPC. Switching from latent to lytic cycle in tumor cells can happened spontaneously, particularly whenthe viral immediate early genes are induced via signal transduction after initial activation by anti-IgG,TGF-ß and CD4+. In NPC, the induction of EBV lytic cycle by cisplatin and irradiation gamma leads tothe increasing expression of BRLF1 and BZLF1 which have a correlation with the increasing of tumorprogression. RT-PCR technique is a very useful for detecting mRNA BRLF1 and BZLF1 gene expressionat the site of primary tumor, while real-time RT-PCR technique is used to measure the mRNA level ofthose genes.Conclusion: Expression of EBV immediate-early lytic gene in the biopsy of NPC primarytumour provides a basic clinical information for NPC diagnosis and therapy more accurately.