The purpose of the study is to determine the effect and optimum dose and evaluate the safety of ferric citrate, administered three times daily (TID) immediately after meals for a total daily dose of 4 or 6 grams for 56 days, on serum phosphate (PO4) levels in subjects with end stage renal disease (ESRD).

Inclusion Criteria:

• Age>18 years and has a diagnosis of ESRD
• On a three-times per week hemodialysis regimen
• On a stable dose of a phosphate-binding agent for at least one month prior to study entry.
• If on vitamin D supplementation or calcitriol, must be on a stable dose for at least one month prior to study entry.
• Hct >= 20%
• Serum Ca level of 8 mg/dL to 10.5 mg/dL

Exclusion Criteria:

• Is pregnant or lactating
• Clinically significant GI disorder
• Has tertiary hyperparathyroidism or is immediately post-operative from a parathyroidectomy (within the first 3 months post-op or the plasma Ca is <7 mg/dL)
• ferritin>800 ng/mL
• Unstable medical condition unsuitable for the study in the opinion of investigator
• Has been treated with an investigational agent within 30 days of enrollment
• Has a history of documented iron allergy or hemochromatosis