In addition to its well-established use for hematopoiesis reconstitution, bone marrow is considered with increasing interest as a possible source of mature cells for adoptive therapies, in particular for the immunotherapy of cancer. Nevertheless, the peculiarities of bone marrow T cells in comparison with those in lymphoid periphery are still largely unknown. In this report, we show for the first time that bone marrow CD8 T cells are in a different activation state than those in peripheral lymphoid organs. Firstly, we observed that mouse bone marrow contains a significantly higher percentage of blasts within the CD8 T cells than either spleen or lymph nodes, yet such enrichment is not due to recent antigenic stimulation. Secondly, when we challenged bone marrow CD8 T cells from immunized mice with their antigen in vitro, they displayed a faster response than those from the spleen. Thus, we suggest that the bone marrow could be a preferential source of CD8 T cells for adoptive therapies in those cases in which highly active effectors are required.