Interleukin-3 (IL-3) is a multipotent hematopoietic growth factor, which exhibits stimulatory effects on leucocytes, reticulocytes and platelets. Due to its pronounced induction of megakaryopoiesis, IL-3 is thought to be a cytokine with the potential to prevent and to overcome chemotherapy-induced thrombocytopenia. We report on four cases (two of metastatic breast cancer, one of metastatic ovarian cancer and one of Hodgkin's disease) with prolonged chemotherapy-induced thrombocytopenia in whom rhIL-3 in combination with either recombinant human (rh) granulocyte macrophage colony stimulating factor (GM-CSF) or rh granulocyte colony stimulating factor (G-CSF) was administered. In all cases, a steady and clinically significant increase in platelet counts could be observed. No major side effects, neither due to the application of rhIL-3 nor due to rhGM-CSF or rhG-CSF, occurred; only flu-like symptoms were seen, which could effectively be treated with paracetamol. This report highlights the efficacy of combined treatment with rhIL-3 plus rhGM-CSF or rhG-CSF in chemotherapy-induced thrombocytopenia, where megakaryopoiesis could be stimulated efficiently by rhIL-3. Based on this experience, the authors conclude that established thrombocytopenia as a major side effect of myelosuppressive chemotherapy should be considered as an indication for the use of rhIL-3 in interventional treatment. Further investigations in this area are encouraged.