An immunohistochemical study by avidin-biotin-peroxidase was performed on paraffin-embedded and decalcified bone marrow biopsies in 31 acute leukemias (19 myeloid and 12 lymphoblastic). The Ulex Europaeus lectin and 14 antibodies (anti-CD45, -CD34, -myeloperoxidase, -lysozyme, -CD15, -CD68, -carcinoembryonic antigen, -factor VIII-related antigen, BNH9, anti-CD45RO, -CD3, -CD20, DBB42 and DBA44) were tested. All acute myeloid leukemias from M0 to M5 type were stained by either the anti-myeloperoxidase or anti-lysozyme antibodies. CD68, CD15 and the carcinoembryonic antigen were respectively expressed in 80%, 40% and 20% of myeloid leukemias from M1 to M5 type. The Ulex Europaeus lectin and the anti-factor VIII-related antigen antibody stained only the M7 leukemia and the anti-CD3 antibody stained only the T acute lymphoblastic leukemia. DBB42 was expressed by 63% of B-lineage lymphoblastic leukemias and CD20 by 36%. No leukemia was stained by DBA44. Immunohistochemistry on bone marrow biopsy can assess the lineage of most acute leukemias with the use of a panel of antibodies such as the anti-myeloperoxidase, -lysozyme, -CD68, -CD20, DBB42, -CD3, BNH9, anti-factor VIII-related antigen antibodies and the Ulex Europaeus lectin.