We recently showed that BZLF1, the gene encoding the Epstein-Barr virus (EBV) ZEBRA protein, was expressed in all eight nasopharyngeal carcinoma (NPC) specimens studied. We present here studies on the expression of EBV lytic cycle genes in the same eight NPC biopsies to determine if production of the ZEBRA transactivator could lead to a complete productive cycle. The tumour lesions exhibit a number of different patterns of limited lytic gene expression. In three out of eight tumours neither BRLF1 nor BMLF1 expression could be detected. Otherwise BMLF1 mRNA was expressed in all the other specimens. Three specimens also expressed BRLF1. Two specimens not only exhibited BZLF1, BMLF1 and BRLF1 transcripts, but also expressed the late gene BLLF1 which encodes the membrane protein gp220. The early gene product BBLF2 could not be detected in any of the eight NPC. However, expression of the late gene encoding the lytic truncated form of LMP1 (D1LMP) was found in seven of the eight NPC biopsies. Thus, it could be suggested that the EBV abortive lytic cycle occurred in most of the NPC studied.