1. Humoral antibody production has been studied in severely irradiated mice treated with isologous (same strain) or homologous (different strain) bone marrow.
2. The two methods of study involved functional end points of humoral antibody production as evidenced by in vivo lysis of rat erythrocytes or by regression of mouse leukosis E.L. 4 in histoincompatible mouse recipients.
3. Humoral antibody production was lost after irradiation and isologous marrow treatment, but recovered partially in two weeks and almost completely in four weeks.
4. Established immunity was not abruptly terminated after irradiation and treatment with either isologous or homologous marrow, although there was premature loss of immunity to rat erythrocytes by the irradiated, isologous marrow-treated mouse.
5. Permanent immunity could not be transferred by isologous marrow or spleen from immunized donors to irradiated recipients.
6. Treatment of mice histoincompatible to E.L. 4 leukosis with histocompatible donor bone marrow failed to establish rejection of the tumor.
7. These studies support the concept that humoral antibody production in irradiated, marrow-treated mice remains a function of the host rather than of the transplanted tissues.
8. These studies failed to clarify the conflicting evidence concerning the mechanism of the late illness that occurs after treatment of the irradiated mouse with bone marrow from a different strain or species.