Abstract: In the present experiment, recombinant human interleukin-11 (rhIL-11) significantly improved the proliferation activity of hematopoietic cells in the human bone marrow cell culture and increased the number of colonies of multilineage progenitor cells. Meylosuppressed mice or rhesus monkeys by chemo-or radiotherapy had higher platelet counts than those of controls after rhIL-11 treatment. rhIL-11 is safe and effective in reducing chemo-and/or radiotherapy associated thrombocytopenia and the need for platelet transfusions in patients who undergo intensive chemotherapy. rhIL-11 is likely to become an effective agent in correcting meylosuppression induced by radiation or chemotherapy