Abstract
1. The pathology of avascular necrosis of bone and its relationship to the radiographic changes are considered briefly. 2. The inadequacy of radiographic examination in the early diagnosis of avascular necrosis is stressed. 3. Methods of early assessment of the residual vascularity of a bone mass are discussed. 4. Details of the principles, methods, and results of using radioactive phosphorus in the diagnosis of avascularity of bone are described. 5. The dangers and technical difficulties of using radioactive substances are discussed. 6. The possibility is envisaged that surgeons may soon be able to determine at the time of emergency operation whether the femoral head is dead or alive.