Leukemic cells from 21 to 197 adult patients with de novo acute myelocytic leukemia (AML) were positive for IL-2R alpha chain (IL-2R alpha), whereas IL-2R beta chain (IL-2R beta), which is responsible for IL-2 signal transduction, was not found on leukemic cells from any of these cases tested. The expression of IL-2R alpha was closely associated with that of adhesion molecules CD4, CD11b and CD22, and endopeptidase CD10. None of the IL-2R alpha (+) AML cells responded to recombinant human IL-2. These data suggest that IL-2R alpha on AML cells may not be involved in cellular proliferation as one of growth factor receptors but may have a role in the control of cell-to-cell interactions.