An evaluation of the usefulness of EDTA treatment for decalcification of murine bone tissue in order to preserve both morphological details and immunologically intact cell surface antigens has been performed. The ABC immunohistochemical staining technique employing monoclonal antibodies to subsets of T-lymphocytes, B-lymphocytes and to Ia antigens was used on frozen sections. Treatment of mouse hindlegs with EDTA for 14 days resulted in an efficient decalcification and good preservation of morphological details. When lymphoid tissues were handled in the same manner monoclonal antibodies, defining Ly 1, Ly 2, L3T4, MAS 034 and Ia molecules, were shown to retain their reactivity comparable to that of directly frozen tissues. In contrast, formic acid, the commonly used decalcification agent, destroyed most of the antigenic reactivity. We conclude that EDTA treatment of non-fixed, bone-containing tissues provides a suitable demineralization procedure in the immunohistochemical study of, e.g., arthritis and periodontitis.