An epithelial tumor cell line, CG1, was established from human nasopharyngeal carcinoma tissues. The CG1 cells are of an epithelial origin as shown by their reactivities with the epithelial-specific antikeratin antibodies and by the presence of the desmosome structure at cell-cell junctions. CG1 cells possess characteristics of tumor cells because these cells are tumorigenic in nude mice and also have reduced serum requirements for in vitro cultivation. The doubling time of CG1 cells is 20 h and these cells have been successfully cultured in vitro for more than 200 generations. The average chromosome number of these cells is 60. Slot and Southern blot hybridizations showed the presence of Epstein-Barr virus-DNA sequences in CG1 cells. This cell line provides us an in vitro system for the study of the role of Epstein-Barr virus in nasopharyngeal carcinoma.