We reported previously that the EBV BARF1 open reading frame encodes a Mr 31,000-33,000 protein (p31) with potential transforming and oncogenic properties. This gene was found capable of transforming both: (a) the rodent fibroblast lines Balbc/3T3 and NIH3T3 into cells producing aggressive tumors in newborn rats; and (b) the human EBV-negative B-cell line Louckes into cells leading to small tumors, which disappeared 3 weeks after injection. Our recent study showed that BARF1 ORF expression may confer the property of immortalization to primary kidney epithelial cells (M. X. Wei et al., Oncogene, 14: 3073-3081, 1997). Because this suggested that BARF1 could be involved in epithelial malignancy, we investigated its transcriptional and translational expressions in Algerian nasopharyngeal carcinoma (NPC) biopsies by reverse transcription-PCR and immunoblotting using rabbit polyclonal antisera prepared against two synthetic peptides corresponding to distinct, predicted epitopes of the BARF1 protein (NGGVMKEKD, amino acids 172-180, and GKNDKEE, amino acids 203-209). The BARF1 ORF was found to be transcribed and translated in >85% of our NPC biopsies, with high p31 protein level detected in several NPC patient biopsies as well as in NPC-derived xenografts. Our observation of BARF1 expression in a large proportion of NPC epithelial cells suggests that this EBV gene might play an important role in the malignant transformation of human epithelial cells in vivo.