This is an adaptive, phase I, randomized, single centre, double-blind dose finding, parallel-group, multi-cohort placebo controlled study of the efficacy and safety of ronacaleret in up to 45 healthy human volunteers. Cohorts of eligible subjects will be studied for periods up to 28 days. Total daily doses of ronacaleret will range from 100mg, up to 400mg and be administered for a maximum of 28days. The first part of this study will evaluate several doses and schedules of ronacaleret, run in parallel, with respect to their ability to affect mobilization of CD34+ cells into the peripheral circulation. In subsequent cohorts of the study we will utilize information obtained from previous cohorts to further refine and optimise those dosing paradigms which show efficacy. For the first cohort of study participants; the study will commence with 6 days of dosing in an inpatient setting followed by 21 days of continued dosing and evaluation as an outpatient, with a series of regularly scheduled visits, with the final visit on day 28. The study period will include evaluations of pharmacokinetic and pharmacodynamic parameters along with standard laboratory and safety evaluations. The second cohort may be treated with ronacaleret for periods ranging from 14 to 28 days in order to optimise the treatment paradigm with respect to pharmacodynamic efficacy. The PK/PD of each group in cohort one will be utilized to make adjustments in the total daily dose, dose frequency and or duration of dosing investigated in cohort 2. Decisions will be made as to dropping doses based on the PK/PD results and any safety considerations. An initial equal randomization amongst groups within the first cohort may be adjusted to allow for other randomization strategies as various doses and schedules are assessed.