Adoptive transfers of lymphoid populations between Ig-congenic strains of mice were performed to evaluate the presence of memory cells in the bone marrow of immune animals. Transfer of immune splenic B cells or immune peripheral blood mononuclear cells effectively transferred antigen-specific IgGl antibody responses of donor origin. In contrast, BM from immune animals did not transfer a memory response. The lack of memory transfer with immune BM was not due to a suppressive activity of BM since (1) Purified antigen-specific B cells from BM did not transfer memory while purified antigen- specific B cells from immune spleen was a potent source of memory cells, and (2) cotransfer of immune BM with a source of memory B cells (immune PB) did not suppress the transfer of memory. Although immune BM did not have cells capable of transferring antigenspecific memory, copious amounts of antigen-specific antibody were spontaneously produced by immune BM in vitro. These studies suggest that the transfer of immunological memory observed in human BM transplant cases may be the consequence of PB contamination of BM preparations when collected.