Juvenile myelomonocytic leukemia (JMML) is a rare myeloproliferative disease of early childhood, that is peculiarly characterized by the ability of bone marrow progenitors to spontaneously proliferate in vitro, giving rise to granulocyte-macrophage colonies. Although the genetic alteration/s leading to JMML development are still unclear, several lines of evidence indicate that the JMML initiating cell (JMML-IC) may belong to the pool of early stem-like hematopoietic progenitors. Increased EVI-1 gene expression has been detected in a number of myeloproliferative disorders including MDS, AML, blast crisis of CML, and more recently in the peripheral blood of some JMML patients. In order to investigate the nature of the cells expressing EVI-1 in JMML patients, we analyzed its expression in CFU-GM obtained from bone marrow and peripheral blood as well as from highly purified CD34+ progenitors. Normal CFU-GM obtained both from bone marrow mononuclear cells and from highly purified CD34+ cells were also analyzed. Overall, our results suggest that the EVI-1 gene may be normally expressed in early hematopoietic progenitor cells and that in JMML patients an expansion of the EVI-1 positive cell population can be revealed within the clonogenic progenitor pool.