In a previous study we have shown that the interleukin-3 receptor alpha chain (IL-3Ra) is over expressed in about 45% of acute myeloid leukemias (AMLs) and this phenomenon was associated with high blast cell counts at diagnosis, high rate of cycling of leukemic blasts and with a worse prognosis. Here we have investigated the immunophenotypic features of 125 AML patients subdivided into three groups (IL-3Rhigh, IL-3Rmiddle and IL-3Rlow) according to the level of IL-3Ra expression. AMLs over expressing the IL-3Ra represent a subgroup of AMLs with a peculiar immunophenotype mainly consisting in the elevated expression of CD34 and several receptor membrane tyrosine kinases, such as c-kit and flt3, and in a usually low expression of myeloidassociated antigens such as CD11b, CD14 and CD15. These findings suggest that IL-3Ra+++ AMLs are blocked at an early stage of differentiation and express at elevated levels several growth factor receptors. It is proposed that these findings may further help to understand the mechanisms involved in the development of high-risk acute leukemias.