Introduction: Transplantation of blood stem cells has become an important procedure for curing malignant and non-malignant diseases. Depending on the donor it can be allogeneic and autologous transplantation and the sources of blood stem cells are bone marrow, peripheral blood and umbilical cord blood. To approve a transplantation, typing of human leukocyte antigens (HLA) of patients and donors is necessary to gain information about their compatibility. Objective: The purpose of this paper is to determine how the donors are chosen through different methods of compatibility searches. Materials and methods: A patient suffering from ALL is in need of a blood stem cell transplantation which is why his family arrives at the Tissue Typing Laboratory where a blood sample is taken. The sample then goes through different serological and DNA methods to determine compatibility. Results: It is determined that the patient and members of his familiy do not match therefore the search continues in the Bone Marrow Database WorldWide . Conclusion: When typing a relative it is usual to search for one who is a match in 6/6 loci (HLA-A, -B, -DRB1). Since HLA genes are haplotypically inherited and the crossing over of chromosomes is very rare in that region, by typing all of the 6 loci it is possible to determine that the donor and the recipient are a match. In case of a non relative donor a match in 10/10 loci is necessary (HLA-A, -B, -C, -DRB1, -DQB1).