The transfer of tetanus toxoid (TT) and diphtheria toxoid (DT) specific immunity was evaluated in 209 short-term (< 120 days postgrafting) and 257 long-term (> 198 days postgrafting) non-boosted recipients after HLA-identical, HLA non-identical and HLA-identical T cell-depleted marrow transplantation. TT or DT immunizations were not given to donors in the 6 months prior to transplant and the recipients received no immunizations post-transplantation. In 209 short-term recipients, 94% and 74% of recipients had detectable anti-TT and anti-DT titers respectively. In long-term recipients, 110 of 210 (52%) who received HLA-identical grafts, 17 of 38 (45%) who received HLA-non-identical grafts, and seven of seven (100%) who received HLA-identical T cell-depleted grafts had anti-TT titers; and 86 of 212 (40%) who received HLA-identical grafts, 11 of 38 (29%) who received HLA-non-identical grafts, and four of seven (57%) received HLA-identical T cell-depleted grafts had anti-DT titers. When compared to non-boosted normal donor and control subjects, the magnitudes of anti-TT and anti-DT titers from the recipients were comparable to controls. These data show that transferred specific immunity is detectable in long-term recipients of T-cell-depleted or HLA-non-identical grafts without immunizations of donors or recipients before or after transplantation.