The Epstein-Barr virus (EBV) is associated with two major human epithelial malignancies, where it is likely to play a role in the malignant phenotype: undifferentiated nasopharyngeal carcinoma (100% of cases) and gastric carcinomas (about 10% of cases). We and others have obtained growth transformation of monkey kidney primary epithelial cells by transfection of viral DNA, especially with the BARF1 gene of EBV (Wei et al., 1997). We now report that the same type of primary epithelial cells can be growth-transformed using EBV particles derived from a nasopharyngeal carcinoma tumor line. Not only can these EBV-infected cells grow over 100 passages, escaping senescence, in contrast to their noninfected counterparts, but they can also survive and proliferate at very low cell density. Several subclones were characterized in terms of viral gene expression. All these clones gave a similar pattern, with detection of EBNA1 and BARF1 proteins but absence of LMP1. CD21, which is the main EBV receptor on B lymphocytes, was not expressed on parental monkey kidney epithelial cells nor on EBV-infected cell clones. This model of epithelial cell transformation will be useful for a better investigation of EBV functions critical for oncogenesis of epithelial cells.