C-KIT, TIE and HKT expression on leukemic cells from patients were simultaneously analyzed using flow cytometry. Consistent with previous reports, leukemic cells from most patients with de novo acute myeloid leukemia (AML) were C-KIT-positive (28/35), while those from patients with B-lineage acute lymphoid leukemia (B-ALL) were C-KIT-negative (0/9). In the B-ALL patients, leukemic cells trom seven patients had one or more myeloid antigen such as CD13, CD15 and CD33. In contrast to C-KIT expression, leukemic cells from only one patient with acute monocytic leukemia were TIE-positive. Similarly, leukemic cells from only two patients (one, B-ALL with t(4;11)(q21;q23) and one, essential thrombocythemia in myeloblastic transformation (ET-MBT)) were HTK-positive. These results suggest that among the three receptor tyrosine kinases, C-KIT is the most useful marker for identifying AML.