With respect to HPTH treatment, this study is a single group, within-subjects, repeated measures treatment trial. With respect to all bone biopsy analyses, the design is a parallel group design with each subject allocated to one of the 3 biopsy follow-up times: 1, 2 or 4 years after initiation of HPTH therapy. Post-baseline biopsy timing will be randomly assigned (1:1.2:1.4, respectively) to each subject, stratified by gender and by menopausal status, when relevant. Changes from baseline (time 0) to 1, 2 and 4-years will be compared. Subjects who were on conventional therapy in the former version of the protocol will also be randomized into the new study design. In contrast to new subjects, whose biopsy is performed at the end of the conventional care run-in period, the pre-conventional care biopsy will be used as the baseline for the those subjects entering the new design after having been on conventional care in the older protocol. Because it is not known with certainty what effects duration of time on conventional therapy will have on biopsy results, randomization will also be stratified on status of prior study participation. The subjects who were on HPTH therapy at the time of the protocol redesign are followed as a separate group under this protocol.