This comparative, open-label, multicenter, parallel-group study evaluated the effect of altitude on the dose requirements of Mircera (methoxy polyethylene glycol-epoetin beta) to achieve a target hemoglobin concentration of 11-12 grams per deciliter (g/dL) in participants with chronic renal anemia in pre-dialysis and dialysis. Four groups of participants, at sea level (below 50 meters) or an altitude above 1800 meters, and pre-dialysis or dialysis, received 50-250 micrograms (mcg) Mircera subcutaneously (SC), according to the local prescribing label.

Inclusion Criteria:

• Adult participants, >/= 18 years of age
• Chronic kidney disease stage III-IV or V
• Probable start of dialysis within 18 months (pre-dialysis group)
• Hemodialysis or peritoneal dialysis in a stable regimen for at least 3 months (dialysis group)
• Adequate iron status
• Females of childbearing potential must agree to use two effective methods of contraception during the study and for at least 2 months following the last dose of study drug

Exclusion Criteria:

• Failing renal allograft in place
• Acute or chronic bleeding within 8 weeks prior to screening
• Transfusion of red blood cells within 8 weeks prior to screening
• Poorly controlled hypertension, defined as hypertension that needs hospitalization to obtain control
• History of seizures, hemoglobinopathies and/or severe liver disease
• Active malignant disease, except for non-melanoma skin cancer
• Immunosuppressive therapy in the 12 weeks prior to screening
• Treatment with any other investigational agent or participation in a clinical trial within 28 days prior to enrolment
• Known hypersensitivity to Mircera (methoxy polyethylene glycol-epoetin beta) or any of its excipients
• Pregnant or lactating women