Bisphosphonates, in conjunction with rehydration, are now the treatment of choice for hypercalcaemia of malignancy. They can also relieve bone pain and improve quality of life as single agent therapy and, in conjunction with systemic anticancer treatments, can prevent skeletal complications and slow down the metastatic process. The clinical effects are greatest and most clearly defined in breast cancer and multiple myeloma, but, theoretically, clinical benefit should be achievable across the entire spectrum of metastatic bone disease. The new biochemical markers for measuring bone resorption are for the first time providing a direct assessment of the effects of treatment on bone. It is hoped that they will enable a more scientific selection of the type, dose and schedule of bisphosphonate required for the best compromise between efficacy, convenience and patient acceptability. We can expect to see a rapid increase in the use of bisphosphonates in malignancy (especially breast cancer and myeloma). Careful assessment of the health-care economics of this new treatment modality is urgently needed.