High dose corticosteroid therapy constitutes one of major causes of osteonecrosis of the femoral head. To examine the early changes of the femoral head induced by corticosteroid therapy, 20 femoral heads were obtained at autopsy and the other 19 femoral heads without having been on steroid were served as controls. Histological examination from steroid treated group revealed that in areas of subchondral bone there were observed necrotic changes of osteocytes. The nucleus was so pressed to one side of the cell as to assume crescent like aspect. When stained with Sudan IV, fat positive materials were found in the osteocyte lacunae. Electron micrographic examination revealed intracellular fat as low electron dense droplets in these degenerative osteocytes. Examination of bone marrow showed an increase of the number of fat cells in steroid treated group. These changes in man may represent some failure in lipid metabolism, although it is unknown whether these events may produce osteonecrosis of the femoral heads.