Endogenous myeloid colony-stimulating factors (CSFs) have demonstrated the ability to enhance the clinical management of immunosuppressed patients with cancer. These agents are associated with significant decreases in chemotherapy-associated infections, antibiotic use, length of hospital stays, and mortality. Two major endogenous recombinant myeloid CSFs currently are being manufactured. Granulocyte macrophage CSF (GM-CSF) (sargramostim, Leukine®, Immunex Corporation, Seattle, WA) has broad activity in the proliferation and differentiation of myeloid lineage progenitor cells, whereas granulocyte CSF (filgrastim, Neupogen®, Amgen, Inc., Thousand Oaks, CA) acts selectively on cells of the granulocyte lineage. Clinical trials suggest that GM-CSF has clinical benefits beyond enhancing neutrophil recovery, including shortening the duration of mucositis and diarrhea, stimulating dendritic cells, preventing infection, acting as an adjuvant vaccine agent, and facilitating antitumor activity.