The primary objective of this study is to compare the urinary excretion of 14C-labeled risedronate and alendronate over 28 days.

Inclusion Criteria:

• have medical history documentation verifying postmenopausal status of at least 2 years (natural or surgical). If not documented, confirmation will be required using estradiol < 20 pg/mL and follicle stimulating hormone (FSH) > 40 IU/mL;
• have osteopenia or osteoporosis (< 1.002 g/cm2 Lunar or < 0.882 g/cm2 Hologic) as determined by DXA of the lumbar spine (AP or PA view, L1-L4). This corresponds to a T-score of approximately < -1.5.

Exclusion Criteria:

• any clinically significant out-of-range laboratory values and vital signs,
• a clinically significant cardiovascular, hepatic, renal, or parathyroid disease, in the opinion of the Investigator
• a known hypersensitivity to bisphosphonates