In the present investigation, the uptake of radio-active phosphorus was studied at different intervals from one week to one year after the fracturing of rat femora. At the same time, the weight of the bone ash was measured. In conformity with previous results, there was an increased uptake of radio-active phosphorus not only at the site of the fracture, but also in the epiphyses of the femur and in the proximal epiphysis of the tibia. While the increase in radio-activity at the site of the fracture was distinct even six months after fracture, the increase in the epiphyses was practically limited to the period between the first and the eighth week. The weight of the bone ash showed a marked reduction, especially as regards the epiphyses of the femur and the proximal epiphysis of the tibia, during the first week after fracturing. This lost mineral substance was replaced during the following weeks in those animals in which fracture healing was good, but not in those animals in which the healing was bad. There was no difference as regards the uptake of radio-active phosphorus between animals with good healing or animals with bad healing.