The introduction of hematopoietic cytokines into the clinic has been rapid with three currently approved by the Food and Drug Administration and perhaps a dozen more in clinical trials. Combinations of cytokines have been relatively unexplored in the clinics. Knowledge about the use of cytokines with chemotherapy has grown considerably in the past few years. The literature relating to use of cytokines in support of standard chemotherapy, marrow failure syndromes associated with malignant disease, and dose intensification not requiring progenitor cell replacement has been reviewed. This review does not address the use of cytokines to support bone marrow transplantation and collection of progenitor cells. Hematopoietic cytokines shorten the duration of cytopenia and decrease infectious complications when used to support standard chemotherapy regimens. However, several randomized trials have failed to show a benefit of such cytokine-supported treatment programs in terms of antitumor response, palliation, or survival. One exception is granulocyte-macrophage colony stimulating factor used with aggressive but standard chemotherapy for high-risk non-Hodgkin lymphoma. Cytokines decrease the infectious complications of myelodysplastic syndromes and may decrease transfusion requirements. Marked escalations in chemotherapy doses are possible with specific chemotherapy regimens. These increase complete remission rates although no benefit in survival or palliation has yet been proven. Cytokines have not been effective in allowing escalation of doses with certain chemotherapy agents and regimens. Cytokines decrease hematopoietic toxicity with standard or escalated chemotherapy doses. Randomized trials are now beginning to define the true patient benefit of this capability.