1. Since avascular necrosis inevitably develops in a certain percentage of patients with fractures of the neck of the femur because the blood supply of the head of the femur has been diminished as a result of the fracture, theoretically one should be able to predict shortly after fracture whether a given patient will have clinical evidence of avascular necrosis.

2. If the circulation of the head of the femur is interrupted, in vivo uptake studies reveal no uptake of P³² ninety minutes or more after injection.

3. Studies of uptake of P³² appear to be of prognostic value in two-thirds of patients with displaced fractures of the neck of the femur. In the group reported here, had these data been used as the deciding factor as to whether a prosthesis should be inserted primarily, an actual or irreversible error would have been made in approximately 10 per cent.

4. In a given patient, the experimental uptake study may not predict the clinical end result accurately either because of failure to obtain data from the weight-bearing area, or because of the presumably insurmountable obstacle presented by irregular isotope uptake in the head of the femur caused by partial interruption of the circulation.