Avascular necrosis of bone has become a well-recognized complication of renal transplantation. While preexisting metabolic bone disease, especially hyperparathyroidism, and metabolic disturbances induced by steroids have been implicated as etiological factors, the pathogenesis is controversial. The diagnosis of avascular necrosis of bone had been based on a history of joint pain and radiographse demonstration of bone necrosis. Recently the bone scan using Tc-99m-methylene diphosphonate is helpful in determining the early stage of bone necrosis. We report two cases of avascular necrosis of femur head, of which diagnosis was made by the bone scan using Tc-99m-methylene diphosphonate.