Transplantation of haematopoietic cells is a procedure performed for the treatment of malignant and non-ma- lignant haematological diseases. Allogenic transplantation can produce antitumour activity through the graft- versus-leukaemia effect. In most transplant patients the course of treatment is complicated by the graft-versus-host disease (GVHD). A successful outcome of transplantation correlates positively with complete donor haematopoiesis (donor cell chimerism), identification of the post-transplant blood cell origin provides evidence not only on engraftment but also on current graft activity and possible rejection during treatment. Application of the polymerase chain reaction (PCR) in molecular biological inves tigation of donor chimerism using a variable number of tandem repeats (VNTR), short tandem repeats (STR) or determination of a number of blood cells containing Y chromosome in the case of sex-mismatched transplantation enables very sensitive, specific and effective estimation of the risk of GVHD development or disease relapse in transplant patients.

        Key words: transplantation, haematopoietic cells, bone marrow, haematopoiesis, chimerism, PCR.