Patients will come to NIH for a physical examination and blood and urine tests every 6 months and for monitoring of their bone disease, vision, hearing, pain levels, functional evaluation, and photographs every 12 months. Many of the monitoring procedures, including imaging studies and biopsies, are performed for the screening protocol (98-D-0145) and will not be duplicated for this study. During the study periods when patients are taking alendronate or placebo, they will have blood samples drawn by their local physician once every 3 months and sent to NIH to check for secondary hyperparathyroidism.