A new scanning dual-photon attenuation method utilizing a 153Gadolinium point source has been evaluated. The method allows precise in vivo determination of the bone mineral content of the lumbar spine (lumbar BMC). Lumbar BMC is expressed as the sum of the scan integrals of the second, third, and fourth lumbar vertebrae. The influence of crush fractures and varying amounts of soft tissue and fat is negligible. The coefficient of variation of repeated measurements ranges from 1.4% in normal pre-menopausal women to 2.6% in post-menopausal women with clinical osteoporosis. The radiation dose is low. The method is suited for cross-sectional and longitudinal studies of patients with lumbar osteopenia.