The purpose of this study is to observe the effects of a treatment strategy that incorporates cinacalcet HCl into the management of secondary hyperparathyroidism (HPT) in subjects with ESRD receiving hemodialysis, on bio-intact parathyroid hormone (biPTH), corrected serum calcium, serum phosphorus, and calcium phosphorus product.

Inclusion Criteria: - Men and women must agree to use highly effective contraceptive measures throughout the study - Prescribed hemodialysis for at least 3 months before study day 1 - Cohort 1: The mean of 2 biPTH determinations obtained from the central laboratory must be greater than 160 pg/mL and less than or equal to 430 pg/mL - The mean of 2 corrected serum calcium determinations obtained from the central laboratory must be greater than or equal to 8.4 mg/dL Exclusion Criteria: - Have an unstable medical condition, defined as having been hospitalized, other than for dialysis vascular access revision, within 30 days before day 1, or otherwise unstable in the judgment of the investigator - Subjects receiving oral vitamin D - Pregnant or nursing females - Parathyroidectomy in the 12 weeks before day 1 - Received, within 21 days before day 1 of the dose titration phase, therapy with medications that are predominantly metabolized by the enzyme CYP2D6 and have a narrow therapeutic index (e.g., flecainide, vinblastine, thioridazine and most tricyclic antidepressants). The antidepressant amitriptyline is permitted - Received, within 21 days before day 1, therapy with medications that are potent inhibitors (e.g. ketoconazole, itraconazole and erythromycin) or inducers (e.g., rifampin and St. John's Wort) of the enzyme CYP3A4. Phenytoin, phenobarbital and carbamazepine are also potent inducers of this enzyme. However, subjects on a stable dose of any of these anti-convulsants at baseline, with no evidence of seizure activity in the past 2 months may be eligible for the study - Experienced a myocardial infarction within 12 weeks prior to day 1 - Other investigational procedures are excluded - Currently enrolled in, or have not yet completed at least 30 days since ending other investigational device or drug trials, or are receiving other investigational agents (experimental dialysis machines are acceptable) - Current gastrointestinal disorder that may be associated with impaired absorption of orally administered medications or an inability to swallow tablets - Participated in other studies with cinacalcet HCl - Disorder that would interfere with the understanding and giving of informed consent or compliance with protocol requirements