The human leukocyte antigen (HLA) system consists of a complex array of genes. HLA antigens are found on the surface membranes of all nucleated cells of the body, including solid tissues, lymphocytes, granulocytes, monocytes, and platelets. The antigens of the HLA system are involved in the rejection of transplanted solid organs, bone marrow and the survival of platelet transfusions. Many HLA antigens have been identified. The NYBC HLA-testing laboratory does HLA typing of individuals and families for the A, B, C and DR genetic loci, as well as HLA antibody screening of leukocytes and platelets.