Patients who have received the appropriate number of years of alendronate or risedronate therapy will be recruited. Each patient will have received baseline BMD measurements performed at the spine and the hip by DXA. Each patient will receive tetracycline to label the bone and then have a transiliac bone biopsy. One year later teh bone label and biopsy procedure will be repeated.

Inclusion Criteria:

• Women at least 5 years postmenopausal
• Subjects treated with any combination alendronate 10 mg daily or 70 mg once weekly or any combination of risedronate 5mg daily or 35 mg weekly for 3-5 years. Or subjects treated with any combination of alendronate 10 mg daily or 70 mg once weekly or any combination of risedronate 5mg daily or 35 mg weekly for greater than 5 years.

Exclusion Criteria:

• Presence of metabolic bone disease other than PMO
• Use of any medication other than alendronate or risedronate within with in the past 6 months likely to interfere with skeletal homeostasis.

Uncontrolled hyperthyroidism. Previous history of malignancy except treated squamous cell or basal cell carcinoma of the skin.

• Alcohol or drug abuse, current or within the past 5 years.
• Allergy to tetracycline, Novocain, or Versed.
• Hip anatomy not conducive to transiliac bone biopsy or DXA scan.
• Previous bilateral transiliac bone biopsies.

Outpatients from bone research centers who have taken alendronate or risedronate for 3 to 5 or more years