Epstein-Barr virus (EBV) infection is found in 7% of Japanese gastric carcinoma. Our strategy is to establish the EBV infected epithelial cell lines from EBV infected gastric carcinomas and to characterize the cell lines on the bases of cellular and molecular biology to define the etiological role of EBV. We have characterized two EBV positive cell lines, GT38 and GT39 from gastric tissues. The both cell lines were EBV latency type III and produced the virus spontaneously. The character of tumor cells was demonstrated by the colony formation in soft agar and the tumorigenesis in severe combined immunodeficient mice.