Purified DNA of Epstein-Barr virus (EBV) is regularly infectious by means of the "calcium" method of transfection. Cultured human placental cells exposed to EBV DNA of two transforming strains, FF41 and B95, produce virus that is capable of converting normal B lymphocytes into established cell lines. After treatment with EBV (FF41) DNA and EBV (HR-1) DNA the placental cells display antigens associated with the productive viral cycle. The placental cells have not developed foci or other signs of morphologic transformation.