Background: In order to investigate the efficacy and safety of recombinant human interleukin-11 (rhIL-11) in the treatment of chemotherapy-induced thrombocytopenia in acute lymphoblastic leukemia. Methods: we conducted a multicenter, randomized, parallel contrast trial of rhIL-11 in 120 patients, of which, 104 patients were eligible for this study. Forty-six patients received rhIL-11 at 50 mu g/kg subcutaneously daily beginning at 24 h after the chemotherapy ended and continuing for 10 days or until platelet counts reaching >= 80x10(9)/L after nadir. Fifty-eight patients in the control group received the same chemotherapy regimen without rhIL-11. Platelet counts were monitored every other day and symptoms of bleeding or infection were recorded. Results: Only 4/46 patients (8.70%) who received rhIL-11 required platelet transfusion versus 14/58 control patients (24.10%, P < 0.05). rhIL-11-treated patients received fewer platelet transfusions than control patients (mean of 7.2 transfusions vs. 11.7 transfusions, P=0.05). The incidence of grade-4 thrombocytopenia was lower in rhIL-11-treated patients (6.5%) than in the control group (20.7%). rhIL-11-treated patients achieved higher platelet counts than the control group after nadir. Conclusions: rhIL-11 at 50 mu g/kg/day beginning at 24 h after the end of chemotherapy was safe and effective for treating chemotherapy-induced thrombocytopenia with mild and manageable side events.