BALB/c mice depleted of T-cells by thymectomy at 3 to 5 days of age and by treatment with antithymocyte serum were inoculated with the lymphatic leukemia virus derived from Friend virus. After a long latent period, these animals developed erythroid leukemia. In contrast, intact control mice inoculated with Friend virus-associated lymphatic leukemia virus developed typical thymic (T-cell) lymphomas. Cell-free virus prepared from leukemic T-cell-depleted animals induced lymphoid, myeloid, and erythroid leukemias in intact mice. The erythroid leukemia-inducing virus differed from the spleen focus-forming component of Friend virus in its long latent period (88 to 225 days) and in its inability to induce spleen foci. End-point dilution experiments suggested that a hitherto undescribed component of the Friend virus complex might be responsible for these late-appearing erythroid leukemias.