Our objective was to evaluate the effects of darbepoetin alfa (Aranesp) on hemoglobin and transfusions in anemic patients with cancer undergoing chemotherapy, and the impact of age, sex, baseline hemoglobin, chemotherapy type, and tumor type. Patients were randomized to one of three darbepoetin alfa groups based on average weekly dose (< 1.5 microg/kg, 1.5 to 2.25 microg/kg, and > 2.25 microg/kg) or to placebo. Dose response was evaluated for change in hemoglobin, hemoglobin and hematopoietic responses, and red blood cell transfusion rates. Hazard ratios for the incidence of hemoglobin response and transfusions were calculated. Adverse events and antibody formation were assessed. Treatment effects were observedfor all hemoglobin end points and incidence of transfusion. The incidence of hematopoietic response among the darbepoetin alfa dose groups ranged from 46% (95% confidence interval [CI] = 33%-60%) to 74% (95% CI = 66%-81%) and increased with higher darbepoetin alfa dose. Patients receiving darbepoetin alfa were more likely to exhibit a hemoglobin response and less likely to require a transfusion, compared with placebo, irrespective of the patient characteristics examined. No increased risk of adverse events and no development of neutralizing antibodies were observed with darbepoetin alfa use. Darbepoetin alfa increased the likelihood of a hemoglobin response and decreased the need for transfusions in cancer patients with chemotherapy-induced anemia.