Over the past two decades, there have been major advances in the therapy of malignancies. One of the major obstacies to the delivery of effective doses of chemotherapeutic agents is the hematopoietic toxicity associated with certain agents. Chemotherapy dose modification, administration of antibiotics and red cell and platelet transfusions have constituted the major means for coping with the hematologic side effects of cancer treatment. Despite the considerable success of these supportive care efforts, myelosuppression is still an important problem both for health care workers and patients. After the successful use of granulocyte colony stimulating factor (G-CSF) as prophylaxis against neutrophilic complications of chemotherapy, attention has shifted to thrombocytopenia and encouraged the clinical investigation of several agents with the ability to stimulate thrombocytosis.Among the variety of thrombopoietic molecules, five agents have now been tested clinically. These are interleukin 1 (IL-1), IL-3, IL-4, IL-11 and IL-3 and GM- CSF fusion protein (PIXY321). Two other molecules IL-3 mimetic (SC55494) and thrombopoietin (TPO) are poised to enter clinical trials. Current information about these molecules are largely confined to toxicity data and very limited efficacy results from phase I investigations.