To update the American Society of Clinical Oncology/American Society of Hematology (ASCO/ASH) recommendations for the use of epoetin. The guideline was expanded to address use of darbepoetin and thromboembolic risk associated with these agents. An Update Committee ("Committee") reviewed and analyzed data published since 2002 through July 2007. MEDLINE and the Cochrane Collaboration Library databases were searched. For patients with chemotherapy-associated anemia, the Committee continues to recommend initiating an erythropoiesis-stimulating agent (ESA) as hemoglobin (Hb) approaches, or falls below, 10 g/dL, to increase Hb and decrease transfusions. ESA treatment continues to be recommended for patients with low-risk myelodysplasia for similar reasons. There is no evidence showing increased survival as a result of ESA treatment. Conclusive evidence is lacking that, absent clinical circumstances necessitating earlier treatment, initiating ESAs at Hb levels greater than 10 g/dL either spares more patients from transfusion or substantially improves their quality of life. Starting doses and dose modifications based on response or lack thereof should follow the package insert. Continuing ESAs beyond 6 to 8 weeks in the absence of response, assuming appropriate dose increase has been attempted in nonresponders as per US Food and Drug Administration-approved labeling, does not seem to be beneficial, and ESA therapy should be discontinued. The Committee recommends monitoring iron stores and supplementing iron intake for ESA-treated patients. ESAs should be used cautiously with chemotherapy, or in clinical states, associated with elevated risk for thromboembolic complications. The Committee also cautions against ESA use for patients with cancer who are not receiving chemotherapy, since recent trials report increased thromboembolic risks and decreased survival under these circumstances.