Four procedures--single photon absorptiometry, dual photon absorptiometry, dual energy radiography, and quantitative computed tomography--allow nontraumatic measurement of bone mineral, with high accuracy and precision, under conditions generally encountered in patient care situations. By using these procedures, almost any part of the skeleton is accessible to such measurements. Total bone is measured by the absorptiometry procedures, trabecular bone by quantitative computed tomography. Several commercial instruments are available for each technique. For clinical use, if decisions are being made based on measurements in a given patient, preferred measurement sites are the spine (for Type I osteoporosis) and hip (for Type II osteoporosis). The newly introduced dual energy x-ray absorptiometry (DEXA) procedure allows measurements of the spine and hip with the highest precision and accuracy, the lowest radiation dose, and the shortest scanning time.