In 249 patients with fractures characteristic of bone fragility, i.e. femoral neck fracture, vertebral crush fracture, fracture of the upper end of the humerus, Colles' fracture, fracture of the lateral condyle of the tibia and various ankle fractures, and forearm bone mineral content was measured by gamma absorptiometry. Vertebral crush fracture, fracture of the upper end of the femur and fracture of the distal end of the forearm are associated with a generally decreased bone mineral mass. In young women with femoral neck fracture the difference between fracture cases and control cases was greater than in older women. In Colles' fracture, the difference from normal controls was the greatest in the youngest and the oldest women. Bone mass in the forearms is low also in cases of fracture in the upper end of the humerus, of the ankle and of the lateral tibial condyle. In each of the above groups, however, there was so much over-lap between fracture cases and control cases that the measurement of mineral in the forearm cannot be recommended as a very good tool for determination of fracture susceptability in individual subjects.