Bisphosphonates are being used in disorders associated with accelerated resorption of bone, particularly Paget's disease of bone and the bone disease of malignancy. Their undoubted biological efficacy and relatively low apparent toxicity make them attractive candidates for the management of osteoporosis. The bisphosphonate alendronate has many characteristics which suggest that it is suitable for use in osteoporosis. It is a potent inhibitor of osteoclast-mediated bone resorption with no adverse effect on the mineralization of bone. Earlier studies have shown it to be one of the most active bisphosphonates in Paget's disease and the hypercalcemia of malignancy. In common with other bisphosphonates tested thus far, alendronate appears to inhibit bone loss in a variety of experimental models of osteoporosis. Long-term studies are needed to determine its steady-state effects on bone mass in man. Most data indicate that alendronate is capable at least of decreasing the rate of bone loss, and might even induce increments in bone mass for many years. Since the experimental studies show that the increase in bone mass observed with alendronate is associated with an increase in bone strength, its use is likely to decrease the frequency of fractures. However, direct clinical evidence for this requires the outcome of well-designed long-term prospective studies.