One of the basic approaches which provides for the increase of immunological safety of hemocomponental therapy is the use of donor-recipient histocompatible blood. The decisive factor in the organism's individuality is HLA-antigen system. Antigen incompatibility of donor's and recipient's tissues in HLA-antigen causes the development of delayed hypersensitivity and sensibilization of the recipient, which provoke a number of complications and posttransfusion reactions. Histocompatibility is the key problem for modern transfusiology and transplantology.