AbstractThe topographical distribution of HLA class I antigens has been investigated by the immunoperoxidase technique on normal frozen thymic tissue sections with a panel of mono‐ and polymorphic monoclonal anti‐HLA antibodies. HLA class I framework determinants detected by the monoclonal antibody W6/32. HL were present on 80–90% of cortical thymocytes, as well as on all cortical epithelial and medullary cells. However the staining intensity of cortical thymocytes with this reagent was about threefold weaker than that of the medullary thymocytes. Labeling patterns of selected monoclonal antibodies against matching HLA‐A/B allospecificities revealed striking variations in the quantitative expression of certain HLA‐Avs.HLA‐B locus alloantigenic determinants on cortical thymocytes compared to a consistent staining on almost all medu