We conducted a study on the utility and safety of rhIL-2 immunotherapy for leukemia. The responses of leukemic cells expressing interleukin-2 receptor (IL-2R) gene obtained from 7 leukemic cell lines, 6 cases of acute lymphoblastic leukemia (ALL) and 8 cases of acute myeloid leukemia (AML) were measured by 3H-thymidine incorproation. The results showed that the responses of these cells were heterogeneous. The cells expressing IL-2R alpha and IL-R beta mRNAs simultanesously from NKL-1,2 cases of ALL and 1 cases of AML(M5) responded to rhIL-2 proliferatively; the cells from 3 leukemic cell lines, 2 cases of ALL and 2 cases of AML were inhibited by rhIL-2; the leukemic cells from the remaining 3 leukemic cell lines and 7 cases of leukemia did not respond to rhIL-2. The study demonstrates that the responses of leukemic cells expressing IL-2 receptors to rhIL-2 are heterogeneous. The patterns of the responses are proliferative, being inhibited to rhIL-2, or irresponsive. So rhIL-2 immunotherapy is suitable for the patients whose leukemic cells were inhibited by or did not respond to rhIL-2 in vitro, but this immunotherapy is not suitable for the patients whose leukemic cells responded proliferatively to rhIL-2 in vitro.