Abstract
An isoantiserum effecting the survival of tumor homografts was produced in mice immunized with an implant of live homologous tumor or of tumor supernatant. The rate of production of antiserum was followed by bleeding the mice at successive intervals and testing serums thus obtained for their ability to insure homograft survival when passively transferred. Peak production of antiserum took place 2-3 weeks after immunization and persisted for at least 8 months.