3. To evaluate changes in the architecture or structure of the bone subjects will have 2 tests. First, the heel images that are obtained during the bone density test (under #2) will be subjected to radiographic texture analysis. This is a method of computerized analysis of the pattern of bone radiographic images which is supposed to differentiate between strong and weak bone based on the difference in the radiographic texture. The second test will be a bone biopsy. A bone biopsy involves inserting a needle through the skin and directly into the bone to obtain a piece of the bone of 1 cm (less than ½ inch) in length and 0.3 cm (1/10 inch) in diameter. Before this biopsy needle is inserted a numbing medication is injected to prevent pain during the procedure. You will also receive a medication through the vein so that you will be almost asleep during the procedure (intravenous sedation). Most people only experience minor pain for a few days after the biopsy. Subjects will have had the first bone biopsy before enrolling into this study. A second bone biopsy will be performed after 12 months of treatment with rhPTH.