Secondary HPT is common in people with end stage renal disease (kidney disease). Patients with secondary HPT often have high parathyroid hormone (PTH) levels and may have large parathyroid glands in the neck. Patients with secondary HPT may have bone disease (osteodystrophy). This bone disease may cause bone pain, fractures, and poor formation of red blood cells. Other problems from secondary HPT may include increases in blood levels of calcium and phosphorus. These may cause calcium to deposit in body tissues. Calcium deposits can cause arthritis, muscle inflammation, itching, gangrene, or heart and lung problems.

The purpose of this study is to evaluate the effects of cinacalcet on bone function and bone cells in patients with kidney disease who are receiving dialysis. Cinacalcet has been used to decrease PTH levels in patients with secondary HPT.

Inclusion Criteria: Subjects will be eligible for the study if they meet all of the following criteria:

• One biPTH determination obtained from the central laboratory must be >/= 160 pg/mL.
• One serum calcium determination obtained from the central laboratory must be >/= 8.4 mg/dL (2.1 mmol/L).
• One BALP determination obtained from the central laboratory must be >/= 20.9 ng/mL.
• Positive histologic confirmation of high bone turnover disease as assessed by the central bone histology center.
• Treated with dialysis for 1 month to 6 months before the date of informed consent.

Exclusion Criteria: Subjects will be ineligible for the study if they:

• Have an unstable medical condition in the judgment of the investigator.
• Are pregnant or nursing women.
• Had a parathyroidectomy in the 3 months before the date of informed consent.
• For subjects prescribed vitamin D, have received vitamin D therapy for less than 30 days before day 1 or required a change in vitamin D brand or dose level within 30 days before day 1.
• Ever received therapy with Sensipar®/Mimpara®