Osteoporosis is a significant disease because it increases the risk of fractures throughout the skeleton, most importantly in the spine and hip regions. The current medications for osteoporosis, which include estrogens, bisphosphonates, raloxifene, and calcitonin, all primarily prevent bone loss, although each may be associated with small bone gains. Another class of drugs, the anabolic drugs, will increase bone formation more substantially, leading to bigger gains in bone mass. One of these, sodium fluoride, clearly increases bone mass but may or may not reduce fracture risk. Another bone-forming agent is human parathyroid hormone (PTH). We and others have demonstrated substantial bone mass gains as well as a reduction in vertebral fracture with the use of PTH administered by daily subcutaneous injection.