Several methods are presently available for measuring the mineral content of bone. Those in widespread use include dual-photon absorptiometry and quantitative CT. The feasibility of using dual-energy digital chest radiography for determination of the mineral content of posterior ribs on digital chest images was studied by using a prototype unit. The results showed a significant difference in the mineral density of the posterior ribs of control subjects and those of patients who had osteoporosis (251.1 +/- 36 mg Ca2+/cm2 of rib vs 158.8 +/- 48 mg Ca2+/cm2, p less than or equal to .01) and a close correlation with values obtained by dual-photon absorptiometry of the lumbar spine (r = .77). The results suggest that this technique can provide an accurate assessment of the presence or absence of osteoporosis.