Abstract
A graft-versus-host reaction induced in (SJL/J x C57BL/1)F1 hybrid mice by injection of SJL/J spleen cells resulted in 100 percent incidence of tumors at 40 days. Transplantation studies revealed that the tumors were antigenically C57BL/1. Since both SJL/J and C57BL/1 mice carry tumorigenic virus, the evidence suggests a viral etiology.