This 2 arm study will compare the efficacy and safety of Mircera and darbepoetin alfa, administered at extended dosing intervals, in the maintenance treatment of anemia in patients with chronic kidney disease (CKD) who are on hemodialysis. Eligible patients receiving once-weekly intravenous (IV) darbepoetin alfa maintenance treatment will be randomized to receive either intravenous Mircera once a month (at a starting dose of 120, 200 or 360 micrograms/month, depending on the weekly dose of darbepoetin alfa prior to start of study) or intravenous darbepoetin alfa every 2 weeks before switching to once monthly administration. The anticipated time on study treatment is 3-12 months, and the target sample size is 100-500 individuals.