Bisphosphonate therapy for the treatment of skeletal complications from osteolytic metastases has become standard care in patients with cancer who have metastatic bone disease. The ability to assess patient response to bisphosphonate therapy has been helped by the availability of immunoassays that can measure bone collagen breakdown products that are increased in the blood and urine of patients with osteolytic metastases. Measurements of the carboxy and amino terminal telopeptides in blood and urine particularly have been helpful as adjunct methods to facilitate the treatment of patients with skeletal metastases. These biochemical bone markers have been shown to correlate with the extent of skeletal involvement and seem to provide a means of monitoring the dose and scheduling of bisphosphonate therapy of patients with cancer who have bony metastases.