The expression of interleukin-2 receptors (IL-2R) was examined in 328 adult patients with non-T-cell (non-T) acute leukaemia and blast crisis of chronic myelocytic leukaemia (CML.BC) using two monoclonal antibodies, anti-Tac for IL-2R alpha chain (IL-2R alpha) and Mik beta 1 for IL-2R beta chain (IL-2R beta). Leukaemic cells in the following cases were positive for anti-Tac; 28/192 of acute myelocytic leukaemia (AML), 24/44 CML-BC, 4/28 CD19(+)CD10(-) acute lymphoblastic leukaemia (ALL), and 20/64 common ALL (c-ALL). IL-2R beta was not detected on leukaemic cells of any case examined. Eleven of IL-2R alpha(+) AML were derived from myelodysplastic syndrome. None of the IL-2R alpha positive leukaemic cells responded to exogenous recombinant human IL-2 (rhIL-2) in culture. In addition, IL-2R alpha expression on non-T leukaemic cells was closely correlated with coexpressing different lineage markers and the presence of the Philadelphia abnormality. Marked increase of serum soluble IL-2R alpha was demonstrated in the IL-2R alpha(+) patients examined. Clinically, the IL-2R alpha(+) patients showed significantly lower response to chemotherapy and poorer prognosis than IL-2R alpha(-) patients. Our results clearly indicate the diagnostic importance of IL-2R alpha expression in non-T acute leukaemia with a close relation to the particular cellular characteristics and the prognosis.