Murine F9 teratoma cells do not express major transplantation antigens detectable by either serologic or alloreactive assays of thymus-dependent lymphocytes (T cells). Such cells can be infected with lymphocytic choriomeningitis virus or vaccinia virus, do express viral antigens on the cell surface, and can release infectious virus in amounts equivalent to those of other H-2 bearing murine cell lines. Immunologic injury of virus-infected F9 cells occurs after the addition of specific antiviral antibody and complement or of specific antiviral antibody and unsensitized lymphoid cells (antibody-mediated cell-dependent killing). In contrast, injury does not follow the addition of immune cytotoxic T cells. These results indicate that possession of H-2 antigens is not a requirement for a cell's infection by or production of virus. Further, expression of viral antigens on the cell's surface, although adequate for antibody-mediated immune injury, is by itself insufficient for direct T cell-mediated lysis. The major transplantation antigens thus probably represent the cell surface structures that are crucial for T-mediated cell wall damage that results in chromium release.