This single arm study will assess the efficacy, safety and tolerability of monthly intravenous Mircera for the maintenance of hemoglobin levels in dialysis patients with chronic renal disease, currently receiving epoetin alfa or beta. Patients will receive monthly intravenous injections of Mircera at a starting dose of 120, 200 or 360 micrograms/month, depending on the dose of epoetin alfa or beta they were receiving in the week preceding study start. The anticipated time on study treatment is 3-12 months, and the target sample size is 100-500 individuals.