The goal of transplant immunology since its beginnings has been, and continues to be, the induction of long lasting unresponsiveness to a foreign graft. Although the transplantation of solid organs and cellular grafts is already a clinical routine, life-long nonspecific immunosuppression is still required to maintain the graft. Malignancies, opportunistic infections and organ toxicity are the main limitations of the antirejection therapy. One approach that finally could make the dream of tolerance induction come true, is hematopoietic chimerism. Hematopoietic chimerism is defined as the coexistence of donor and host hematopoietic cells in the recipient's system. This coexistence might induce the mechanisms of central or peripheral tolerance to foreign, donor's antigens. The aim of this paper is to present current knowledge about relationship between the state of macro- or microchimerism and transplantation tolerance in bone marrow and organ transplantations.