Dual photon absorptiometry with 153Gd was used to determine the bone mineral content of the lumbar spine of 46 subjects. The bone mineral content of the radius and ulna were measured on these same subjects using single photon absorptiometry. The bone mineral content at the peripheral sites was not a very accurate indicator of absolute bone mineral content in the spine. However, the rate of bone loss with age was greater in the peripheral bones than in the spine. Measurement sites on the appendicular skeleton may provide a more sensitive indication of age changes in bone mineral content throughout the skeleton than would sites on the axial skeleton.