HLA-A, with HLA-B and HLA-C, belongs to major histocompatibility complex (MHC) class I antigens and expresses constitutively on all nucleated cells. MHC class I antigens play a role in class I MHC-associated antigen presentation, inhibition of NK cell cytotoxicity, tumor surveillance, and tissue allotransplantation. This MAb is useful for HLA molecular typing of peripheral blood leukocytes as well as a large number of leukemic cell lines. It reacts with an intralocus determinant present on a limited number of HLA-A locus-encoded gene products (HLA-A2, -A3, -A28, -A29, -A30, -A31 and -Aw33). Its epitope maps between aa65-to-aa80 of the α1 domain of the HLA-A. This MAb recognizes an intralocus determinant present on a limited number of HLA-A locus-encoded gene products (HLA-A2, -A3, A28, -A29, -A30, -A31 and -Aw33). Furthermore, by testing its reactivity with HLA-A2 natural variants and mutants, the importance of amino acid residues 79 and/or 80 of the α1 domain was demonstrated in the formation of an intralocus HLA-A determinant.