The diphosphonates are a group of phosphate compounds which inhibit the growth and dissolution of apatite crystals. These drugs have similar biological effects on bone by inhibiting the osteoclasts, and are also active in preventing pathological calcifications. The diphosphonates have been used successfully in various bone diseases and are now currently used for bone scanning. They are also considered one of the best treatments for Paget's disease. Several experiments in vitro and in vivo have suggested that the diphosphonates are active against bone metastases. Clinical trials have been undertaken and have shown that these compounds are active against malignant hypercalcemia. Further, they may delay the extension of bone destruction due to malignancy.