In trying to contribute to our knowledge on the biology of hematopoietic stem cells (HSC) and hematopoietic progenitor cells (HPC) from pediatric acute myeloid leukemia (AML), in the present study we analyzed the expression of four cell surface antigens relevant to human hematopoiesis-CD90, CD96, CD117, and CD123-in bone marrow from pediatric AML patients and normal control subjects.CD34(+) CD38(-) cells (enriched for HSC) and CD34(+) CD38(+) cells (enriched for HPC) were resolved on the basis of CD34 and CD38 expression. Concomitantly, expression of CD90 and CD96 or CD117 and CD123 was assessed by multicolor flow cytometry in each cell population.CD90 and CD117 were expressed in a low proportion of CD34(+) CD38(-) and CD34(+) CD38(+) cells and no significant differences were observed between normal marrow and AML at diagnosis. In contrast, CD96(+) cells and CD123(+) cells were found at significantly higher levels in both cell populations from AML at diagnosis, as compared to normal marrow. Levels of both cell surface markers after treatment remained higher than in normal marrow.These results show an increased frequency of CD96(+) and CD123(+) cells within the CD34(+) cell population from pediatric AML; this is consistent with the findings reported previously for adult AML. Our study supports the notion that expression of such antigens should be explored for their use as markers for diagnosis and prognosis.