Introduction: HLA system was discovered by the middle of the 20th century. Antigens or HLA (Human Leukocyte Antigens) molecules have as their primary role to identify foreign from own molecules in order to initiate an immune response to foreign antigens and to maintain integrity of its own organism. Key function of the HLA genes is in the immune response and the transplant clinical process through the function of its most significant products - HLA molecules. They are the main part of the antigen presentasome complex on the surface of the cells and have as their function to show its own as well as foreign peptide units to cytotoxic and helper T-cells. Scope: the scope of this thesis was to demonstrate the basic significance and function of the HLA system and the responsibility of bachelors of nursing in performing tasks pertaining to diagnostics in this area. Methodology: methods used to determine antigens and alleles of the HLA system are: serological method (microlymphocitotoxicity test) and methods of molecular biology: PCR-SSP and PCR -SSO. Results and discussion: Since the HLA transplant system was discovered it has become the go to choice for treatment of many hematological diseases. The development of methods to determine genes and antigens of the HLA system has increased the success rate of transplanting blood forming stem cells. The improvement of methodology in molecular biology brings forward new insight into greater complexity of the HLA system.