The present invention relates to mammalian hematopoietic facilitatory cells (FC). In particular, it relates to the isolation, characterization and uses of the FC. The FC of the present invention can be distinguished from all other known bone marrow cells by their morphology, cell surface phenotype and in vivo function. It has now been established that purified hematopoietic stem cells alone or bone marrow cells depleted of FC do not readily engraft in a recipient. When co-administered with other bone marrow cells, especially the hematopoietic stem cells into a recipient, the FC enhance their engraftment, without apparent adverse biologic activities. In fact, the ability of the FC to enhance the engraftment of bone marrow cells in esablishing lymphohematopoietic chimerism without producing graft versus host disease also induces donor-specific tolerance to permit the permanent acceptance of donor's cells, tissues and organs. Therefore, FC may have a wide range of applications, including, but not limited to, hematopoietic reconstitution by bone marrow transplantation for the treatment of cancers, anemias, autoimmunity, immunodeficiency, viral infections and metabolic disorders as well as facilitation of solid organ, tissue and cellular transplantation.