Multicenter, open label single arm study in which 140 subjects with CRI who are currently receiving SC darbepoetin alfa once every other week will receive darbepoetin alfa once every 4 weeks for 24 weeks. Upon enrollment into this study, subjects will receive darbepoetin alfa once every 4 weeks for 24 weeks. The initial dose will be equivalent to the subject's total dose in the month preceding enrollment. Doses may be titrated to maintain the Hb concentration in the target range.

Inclusion Criteria:

• Greater than or equal to 18 years of age
• CRI with a creatinine clearance of greater than 15 but less than 40 mL/min
• Stable once every other week darbepoetin alfa SC for at least 6 weeks
• Hb values during screening / baseline of 10.0 - 12.0 g/dL
• Serum B12 and folate levels above the lower limit of normal and iron replete

Exclusion Criteria:

• Receiving renal replacement therapy
• Uncontrolled hypertension
• Hyperparathyroidism
• Major surgery, active inflammatory disease, receiving antibiotics, HIV-positive
• Current malignancy
• Pregnant or breast-feeding