The recent development of noninvasive techniques to measure bone mass and bone turnover represents a major advance in the diagnosis and management of osteoporosis. The rate of formation or degradation of the bone matrix can be assessed either by measuring a prominent enzymatic activity of the bone-forming or resorbing cells, such as alkaline and acid phosphatase activity, or by measuring bone matrix components released into the circulation during formation or resorption. Recent studies have shown that the appropriate combination of the most efficient markers of bone resorption and formation will provide a powerful tool in the clinical investigation of osteoporosis.