The ability of in vivo and in vitro tetanus toxoid (TT) antigen-specific antibody production after the primary immunization with TT vaccine was examined in 5 healthy adults and 3 long term survivors after HLA-identical allogeneic marrow grafting. Serum IgG anti-TT antibody titers became positive in 5 healthy adults but in only one of 3 patients. In vitro spontaneous IgG anti-TT antibody production was detected in 5 healthy adults but only one of 3 patients. In vitro TT antigen-dependent antibody production was detected in 5 healthy adults but only one of 3 patients and the pattern of the patient was different from one of healthy adults. These data indicate that long term survivors after marrow grafting are still disturbed in the ability of in vivo and in vitro TT antigen-specific antibody production after the primary immunization with TT vaccine. It is suggested that impaired spontaneous TT antigen-specific antibody producing B cells and TT antigen-specific memory B cells participate in the impediment.