The density of the distal radius in the non-dominant forearm was measured non-invasively by Compton spectrometry in 234 post-menopausal women. The density of the trabecular tissue was determined almost independently from that of cortical tissue by horizontal and vertical scanning of the bone. It was found that the lower the density of the trabecular bone, the greater the difference between the density of the cortical and trabecular bone. As osteoporosis progresses, trabecular bone density in the distal radius seems to decrease faster than that of compact bone. Hence the severity of the disease is best determined by measuring the density of trabecular bone.