In the United States, darbepoetin alfa (Aranesp) is often used to treat patients with chemotherapy-induced anemia using weekly or every-2-week administration schedules. In Europe, darbepoetin alfa is used either weekly or in every-3-week dosing. The every-3-week schedule can be synchronized with many chemotherapy regimens, resulting in fewer visits and reducing burden to patients, but the safety and efficacy of this regimen have not been clear. A randomized, double-blind, double-dummy, active-controlled phase 3 trial was performed in 110 European centers. Eligible patients (age > or = 18 years) were anemic (hemoglobin level < 11 g/dL), had a nonmyeloid malignancy, and were to receive at least 12 weeks of chemotherapy. Patients were randomly assigned 1:1 to darbepoetin alfa treatment every 3 weeks (500-microg dose) or weekly (2.25-microg/kg) for 15 weeks. We compared red blood cell transfusion incidence among the two arms from week 5 to the end of the treatment phase using a noninferiority study design. Noninferiority was determined if the upper limit of the 95% confidence interval (CI) for the difference in blood transfusions between groups, calculated using Kaplan-Meier methods, did not exceed 12.5%, a margin based on previous placebo-controlled studies. A total of 705 patients were randomly assigned, and 672 remained in the study at week 5. Fewer patients in the every-3-week arm than in the weekly arm received blood transfusions from week 5 to the end of the treatment phase (unadjusted Kaplan-Meier estimates = 23% versus 30%, difference = -6.8%; 95% CI = -13.6 to 0.1). Percentages of patients achieving the target hemoglobin level (> or = 11 g/dL, consistent with evidence-based practice guidelines) were 84% (every 3 weeks) and 77% (weekly). The frequency of cardiovascular/thromboembolic adverse events was 8% in both groups, and safety was comparable. Patients with chemotherapy-induced anemia can safely and effectively be treated with 500 microg of darbepoetin alfa every 3 weeks.