We have studied gene expression of GATA-1, GATA-2, and SCL, which are known as cell-specific transcription factors, in 110 various leukemias consisted of 76 patients with acute myeloid leukemia (AML), 19 with acute lymphoblastic leukemia (ALL), and 15 with chronic myeloid leukemia (CML) in blast crisis by the revearse transcription-polymerase chain reaction assay. Accordingly, we divided into three groups. Group I (GATA-1+SCL+): patients with AML exhibiting phenotypic characteristics of erythroid or megakaryocytic lineage and most of CML myeloid blast crisis were included. Group II (GATA-1+, SCL-): Not only CD7-positive and CD19-positive AML, but also a part of Ph+ALL demonstrated this pattern. Leukemia in this group is considered to have a capability to differentiate into myeloid and lymphoid lineages. Group III (GATA-1-, SCL-): patients in this group consisted of leukemias which are differentiated into specific cell-lineages, either myeloid or lymphoid, when compared to groups I or II. Our data suggest that the expression pattern of transcription factors reflects lineage potential in leukemia cells, leading to classification of leukemias.