The epitopes Tn and sialosyl-Tn are expressed on erythrocytes of individuals with a very rare blood group, who often suffer from "Tn syndrome." We surveyed expression of Tn and sialosyl-Tn in normal blood cells, malignant transformed cells, and progenitor stem cells from bone marrow (BM). An anti-Tn antibody, IE3, and an anti-sialosyl-Tn antibody, TKH2, were used in this study. TKH2 reacted with erythroblasts, B cells, and a subset of CD4+ cells; but not with erythrocytes. Erythroblastic cell lines (K562, HEL, and UT7/EPO) and B-cell lines (Daudi, Raji, and B-cell lines transformed by Epstein-Barr virus) showed reactivity to TKH2. Similar results from the reactivity of TKH2 with transformed cells from leukemia patients and lymphoma patients were obtained; TKH2 reacted with blasts from erythroleukemia (M6; for 4 of 4 cases) and with lymphocytes from B-cell chronic lymphocytic leukemia (3 of 3), B-cell lymphoma (5 of 5), and CD4+ adult T-cell leukemia (4 of 4), but did not react with blasts from acute myeloid leukemia (M0 to M5; 0 of 22) or acute lymphoid leukemia (B-lymphoid leukemia, 0 of 11; T-lymphoid leukemia, 0 of 2; undifferentiated leukemia, 0 of 1). IE3 did not react with all of the tested cells. CD2-CD19-TKH2+ normal BM cells (BMC) contained blasts and various maturation stages of erythroblasts. The TKH2+ cells produced a large number of colony-forming unit-erythroid (CFU-E) colonies, whereas they produced a small number of burst-forming unit-erythroid colonies and CFU-granulocyte-macrophage colonies. CD34+ normal BMC did not express Tn and sialosyl-Tn. These findings suggest that sialosyl-Tn expresses in CFU-E to erythroblasts.